The mystery manual R129 SL600 was first spotted on TikTok, but we managed to track down Georgopoulos and get the story about the manual conversion directly from him. Of course, it started with him being a serious enthusiast of the R129 Mercedes SL600. He says he’s owned 20 of them, but always wanted one in manual. Only the straight-six models get the option of a dogleg five-speed, while the V8-powered SL500 and the V12 SL600 came automatic only. Georgopoulos went out and solved the problem himself.
Eight months of research and development with his partner Bakowski resulted in a conversion that “works as factory.” They used the stock ECUs and recoded them fully to run the gearbox correctly. This includes making the ABS module talk to the engine properly and allow traction control, stability control, and cruise control to work properly. It even uses the stock throttle bodies and “spoofs no signals” to achieve a factory-perfect manual conversion. The engine is stock, but they removed the secondary muffler and installed a Renntech rear muffler to make it sound like a Pagani.
Software is only half of the sauce, though arguably the more difficult side. The hardware they used is a bit more conventional but effective. A ZF GS6 gearbox, ubiquitous in BMWs, is bolted to the V12 with an adapter plate. Sandwiched in between the gearbox and the V12 is a custom six-puck ceramic clutch and lightweight single-mass flywheel. Georgopoulos says customers who’d prefer a less aggressive clutch can option an organic friction material instead. Finally, a custom driveshaft attaches the gearbox to the stock rear differential. Inside, an R129 300SL pedal box and shifter surround keep things totally factory, as does a factory clutch master cylinder.
The work is immense, and the goal was to have a factory-like driving experience. So while the $30,000 is a steep price, it takes a lot to develop and sell a kit like this. With SL600s trading at around the same price as the conversion, it is a lot to swallow. But where else can you get a manual V12 convertible that sounds like a Pagani for $60,000?