Your definitive 1990-2002 Mercedes-Benz R129 SL buyer’s guide

The R129-generation Mercedes-Benz SL, which arrived for 1990, was a long time coming. Its predecessor, the R107-generation SL, had enjoyed a nearly 20-year reign as the preeminent four-wheeled symbol of success, but by the end of the 1980s it was an old car. When the new SL made its debut at the Geneva auto show in early 1990, buyers were more than ready to greet it. Orders poured in, and the first-year production of 20,000 units quickly sold out.

That the R129 SL was radically different from its forebear was no surprise given the age of the preceding model and the fact that Mercedes-Benz was never an automaker to worship at the altar of history. Although the new SL did retain its roadster configuration—with a soft top and a removable hardtop—as well as its six-cylinder and V-8 engine offerings, it was in every other way a truly all-new and forward-thinking design.

Today, this generation SL is a remarkably modern classic in its sophistication, road manners, and equipment. And this paragon of German engineering is startlingly affordable. Here’s what you need to know if you’re thinking about buying an R129 Mercedes-Benz SL.

Models and years

This generation SL can roughly be divided into three segments: early cars, from 1990 through ’95 model years; mid-years models, from ’96 through 1998; and later versions, from 1999 through 2002.

The car arrived for the 1990 model year in two forms: The six-cylinder 300SL and the V-8 500SL. The 300SL was powered by the M104 3.0-liter inline-six, a DOHC, 24-valve design good for 217 horsepower. It could be had with a five-speed automatic transmission or a five-speed manual with a dogleg shift pattern (it is believed only 166 stick-shift examples were sold in the U.S.). For 1994 the engine was enlarged to 3.2 liters, and output climbed to 228 horsepower and 232 pound-feet of torque, but the manual transmission was dropped. The six-cylinder engine would last through 1997.

The 500SL V-8 was the 5.0-liter, 32-valve, DOHC M119 unit, good for 322 horsepower—making it the most powerful engine in a Mercedes-Benz road car up to that time. In 1993, a new version of M119 switched to Bosch LH-Jetronic fuel injection in place of Bosch KE-Jetronic, and output fell to 315 ponies. A 1996 update brought more changes to the engine room. The V-8 got individual ignition coils for each cylinder, a redesigned crankshaft, lighter pistons, and a modified engine-management system. A five-speed automatic replaced the previous four-speed. 1999 and later models switched to the M113 24-valve SOHC V-8, making 302 horsepower and 339 lb-ft of torque.

The 12-cylinder 600SL arrived for 1993. The M120 6.0-liter V-12 made 389 horsepower and a robust 420 lb-ft torque. But its factory-stated zero-to-62-mph time was only 0.1 second quicker than the V-8 car (6.1 second versus 6.2), and it had the same governed top speed of 250 km/hr. Like the V-8, the V-12 was upgraded from a four-speed to a five-speed automatic for ’96.

European buyers had AMG-fettled special editions—the 350-hp SL60 and the 525-hp SL73—but there would be no AMG-branded SL sold in the States until the following generation.

Mercedes-Benz reversed its naming logic for 1994, putting the model designation first, followed by a number denoting engine displacement. For the SL, that meant SL320 (owing to the concurrent displacement increase to 3.2 liters), SL500, and SL600.

Design

Legendary Mercedes-Benz design chief Bruno Sacco has called the R129 SL his “most perfect car,” and the early models are the purest execution of that work. Compared to the preceding model, brightwork is almost completely absent—the three-pointed star centered in the grille is the only chrome element. The long hood and steeply raked windshield telegraph the SL’s position as an exotic roadster, while the swept-back grille and smooth flanks show its fealty to aerodynamics. Early cars had horizontally ribbed taillights, a trio of horizontal slots behind the front wheels, and the bumpers and lower body cladding in a matte finish painted a different hue than the rest of the body (with the exception of Signal Red).

The 1996 revision brought an end to the two-tone color scheme. It also saw a modified grille with fewer bars, new 12-hole alloy wheels, reshaped front and rear bumpers, changes to the front signal lights and taillights, and altered side fender vents. A hardtop with a glass roof panel was a new option, as were HID headlamps. Inside, the seats, steering wheel, and door panels were modified. An optional Sport package became available mid-year, which is visually distinguished by staggered-width 18-inch AMG monoblock wheels, more-sculpted rocker panels, and projector-beam foglights.

In addition to the aforementioned powertrain changes, the ’96 model year also saw the introduction of stability control (ESP), which was an option on the SL500 and standard on the SL600. At the same time, Brake Assist, which increases braking response in emergency situations, made its debut on the R129 SL.

The last significant model update was for 1999. The SL320 was dropped. Final cars had more rounded sideview mirror caps, two slots behind the front wheels, a new 17-inch standard wheel with a five-hole design, and color-keyed door handles. Richer, Nappa leather was standard, though some claim it’s not as long-wearing as the previous hides. There was also a new head unit for the audio system, although it still didn’t include an in-dash CD player. The Sport package was made standard in 2001. The Silver Arrow—available as an SL500 and an SL600—was a fully loaded special edition for the R129’s run-out model year of 2002.

Engineering

That the R129 SL was far more advanced than its predecessor was to be expected, but even compared to its contemporaries, this car was on the technological vanguard. Certainly, that’s evident in the field of safety: The SL had a first-of-its-kind roll bar that deploys automatically in 0.3 second if a rollover is detected (or can be popped up with a switch). Dual front airbags were standard, as were antilock brakes; traction control (ASR) appeared for 1991, as did an electronically controlled limited-slip differential (ASD). Stability control would arrive in 1996, and the SL also was among the first convertibles to get side airbags that same year.

Early models (pre-’96) had, in addition to power-adjustable sideview mirrors, a power-operated rearview mirror (as did the W140 S-Class), a bit of engineering overkill that allowed the inside mirror position to be saved as part of the memory function, along with that of the side mirrors, the power-adjustable steering column, and the seats. Those power seats, by the way, had magnesium frames and five different electric motors, including one to raise and lower the headrests; they also were innovative in that the seatbelts were integral to the seatbacks. The power top was fully automated—including the latches at the windshield header—and disappeared under a hard boot. And there’s more: The central locking system also could lock the various interior stowage cubbies, allowing valuables to be secured even in a car parked with the top down. And an adaptive damping system was offered (it was standard on the V-12 models).

Service

As the above list suggests, the R129 hails from the cost-is-no-object era of Mercedes-Benz product development, when the cars were engineered to a (lofty) standard and not to a price. Though the SL is dauntingly complex it’s also mechanically robust. Being a Mercedes-Benz, many OEM parts are still made, thanks the brand’s commitment to keeping its vintage models on the road via the Mercedes-Benz Classic Center. Note, however, that many interior trim parts are available only in black, something to keep in mind if you’re looking at a car with a sun-roasted interior.

Of course, factory parts and Mercedes dealer service can be punishingly expensive. Finding an independent shop that is comfortable working on these cars can go a long way toward making ownership financially viable. And, as always, starting with a well-maintained example is key.

There are several problem areas to be aware of. The convertible top uses 11 (or 12, depending on the model year) hydraulic cylinders, and these eventually can leak. Replacing the full set at a dealership can run $8000 or $9000, but rebuilt units—using better materials than the original—are available, and can be installed by a knowledgeable independent shop or even by a patient do-it-yourselfer. Tophydraulicsinc.com sells a full set for $550 (plus exchange).

The R129 SL is among the early-‘90s Mercedes models afflicted with degradation of wiring harnesses made from biodegradable materials. There are multiple harnesses, but the most accessible one is under the plastic engine cover; its condition is generally a good indicator of that of the others. Look for flaking on the wiring harness coating or it being brittle. According to Hans Peter Ganz, of Xaver’s auto service in Newburgh, New York, the main harness is $900 to $1500 for the part alone, plus three-to-four hours labor to replace. These harnesses are found in 1995 and earlier cars only, although cars with the 3.0-liter engine do not have the issue.

Speaking generally, Ganz characterizes the M104 inline-six as susceptible to head-gasket leaks, and says both the six and the V-12 are more prone to oil leaks than are the V-8s. The ADS adaptive damping suspension that was standard in V-12 cars (and available in the others) can have accumulators go bad. 1996 and later models are OBD2, which makes diagnosing electrical issues easier. The distributorless ignition system that arrived for the same year is considered more reliable than the previous system.

Valuation

The R129 SL was one of the last Mercedes-Benz models developed under cost-plus philosophy of product development, and that was evident in the pricing of the new car, which shot up over that of the outgoing SL. In 1990, the 300SL was $73,500 (before destination charges or the gas-guzzler tax) and the V-8 version was ten-grand dearer; by 1992, the 300SL was $83,500 and the 500SL was just shy of six figures. When the V-12 arrived, it started at $119,500. The cruel hand of depreciation has brought the market value of these SLs far from those lofty heights.

According to the Hagerty Valuation Tool, the R129 SLs have now begun to climb out of the basement, with the latest update showing price increases of 19 to 31 percent—though they’re still far behind the R107 560SL. The most affordable variant is the early 300SL ($16,600 for a 1990 SL300 in #2 condition), while the later SL600 is the priciest ($26,600 for a 2000 SL600 also in #2 condition). As a rule of thumb, six-cylinder models bring less money than V-8s, which in turn are cheaper than V-12s.

Generally, prices increase as one moves through the model-year range from earlier to later. Of course, an exceptional example will always command an exceptional price: The Mercedes-Benz Classic Center in Irvine, for example, at this writing has a 1990 500SL with just 422 miles from new, at an asking price of $75,000.

Desirable options include heated seats (they were standard on the V-12), “ADS” automatic locking differential, 18-inch AMG monoblock wheels, HID headlights, and the Panorama tinted-glass hardtop. Besides the aforementioned 2002 Silver Arrow, other special models included SL320 and SL500 40th Anniversary Editions for 1997—they commemorated the first 300SL roadster. The SL320 was available in special Quartz Blue Metallic with a dark blue soft top and a gray interior featuring “Exquisite” leather and royal maple wood trim. The SL500 Anniversary Edition was offered in Crimson Metallic with a black soft top over Parchment, with chestnut wood trim. Both include the optional CD changer and heated seats. The SL320 was limited to 250 units, while 500 examples of the SL500 were sold.

The designo Black Diamond Edition (metallic black paint, red-and-black Nappa leather, black carbon-fiber trim), and the designo Slate Blue Edition (slate blue metallic paint, dark-blue-and-black Nappa leather, black carbon-fiber trim) were offered for 2000 and 2001. Also in 2001 was a Formula One Edition, just 20 of which were made to celebrate MB’s return to F1 racing (in the US Grand Prix). All were Brilliant Silver with a silver-gray soft top over black, and special interior features included silver-painted wood trim, bi-xenon headlamps, and engine-turned accents.

Total production of the R129 SL was 204,940, which falls short of the 237,287 examples of the previous, R107 model, but made it much more successful on a sales-per-year basis. All of which is to say that the cars are plentiful, and given that they’re two-seat convertibles marketed to a wealthy clientele, low-mileage, well-cared-for examples aren’t hard to find.

Much more of a grand tourer than a nimble sports car, the R129 is an accomplished mile-eater that pampers its driver and passenger. And the convenient well-insulated convertible top, handy stowage area behind the front seats, and fairly generous trunk make the SL an exceptional road-trip vehicle.

The six-cylinder cars are considerably lighter than the other models, and for that reason come closest to passing for a sports car—particularly when equipped with the manual transmission. But know that the six-cylinder cars are geared shorter than their V-8 and V-12 counterparts, so the engines can rev fairly high at highway speeds (3250 rpm at 70 mph). The inline-six, though, is exceedingly smooth, and needs to be revved to feel responsive anyway. The V-8 is a capable all-rounder, and was by far the most popular variant. The V-12 may not be much quicker than the V-8 off the line, but the sound of this engine is something special, as is the effortless response provided by its deep reserves of torque.

The R129 Mercedes-Benz SL offers a whole lot of highly engineered fabulousness for what is now pennies on the dollar. As Automobile’s Georg Kacher, put it in July 1990: “If perfection bores you, shop elsewhere. But if you want an effortless, comfortable, well-equipped, and sporty open-top tourer that is made to last, look no further.”