Image Credit: Rich Rebuilds / YouTube.A twin-turbocharged V12 Mercedes-Benz S-Class that once cost around $140,000 was recently brought back to life for far less than anyone expected. YouTuber Rich Rebuilds acquired the non-driving luxury sedan in exchange for a used iPhone and set out to determine whether it needed a complete transmission.The car arrived with a long list of problems, including a dead battery, collapsed suspension, leaking coolant, damaged wheels, and a broken oil cooler. Even after the engine was running, selecting Drive or Reverse produced no movement, making a failed transmission seem like a very real possibility.Rather than immediately replacing the gearbox, Rich and his team began diagnosing the car one system at a time. Their work uncovered several neglected maintenance issues, but the transmission fault ultimately came down to a relatively inexpensive electronic component.AdvertisementAdvertisementAfter replacing the conductor plate and servicing the gearbox, the large Mercedes drove normally under its own weight. The part responsible for restoring the transmission cost only $50 after a core refund, turning what looked like a catastrophic repair into a surprisingly affordable fix.A Cheap V12 With Expensive ProblemsThe Mercedes had been purchased for the equivalent of approximately $1,100, but its low price reflected years of neglect. Its suspension was flat, the wheels were badly bent, and the cooling system was losing fluid almost as quickly as it could be added.A pressure test revealed that one of the coolant hose connections had not been seated correctly. Cleaning the fitting, inspecting the O-ring, and reinstalling the hose allowed the system to hold approximately 15 psi without leaking.The oil cooler presented a different problem after a used replacement arrived with damaged threads. Instead of installing the unusable part, the team created a temporary hose-based repair and later received a partial refund that reduced the cooler's final cost to $50.Transmission Diagnosis Revealed a Cheaper FailureImage Credit: Rich Rebuilds / YouTube.Attention then turned to the transmission, which would not engage any gear. The first inspection showed that the gearbox was low on fluid, while the remaining oil appeared dark and heavily contaminated.AdvertisementAdvertisementRemoving the pan revealed a buildup of metallic sludge on the magnet, although there were no obvious signs of catastrophic internal failure. The electrical connector was also soaked in transmission fluid, suggesting that the transmission's conductor plate and connector sleeve were likely involved.The conductor plate sits inside the gearbox and helps control shift functions through a network of sensors and solenoids. When it fails, the transmission may refuse to select gears or enter a protective operating mode that makes a complete replacement appear necessary.A $50 Part Brought the Mercedes BackRich purchased a remanufactured conductor plate assembly for $100 and received a $50 core refund after returning the old component. A new filter, pan gasket, connector, and fresh transmission fluid were installed at the same time.Once the repairs were complete, the Mercedes successfully engaged Park, Reverse, and Drive while raised on a lift. The real test came after the car was lowered, where it accelerated cleanly and continued shifting under load without slipping or losing power.AdvertisementAdvertisementThe successful road test confirmed that the transmission itself had survived. What initially looked like a multi-thousand-dollar gearbox replacement was instead resolved through a $50 electronic component and a thorough service.The Full Revival Still Required WorkImage Credit: Rich Rebuilds / YouTube.Although the transmission repair was inexpensive, the entire revival cost considerably more. New fluids, service parts, replacement wheels, suspension fluid, and the oil cooler brought the project's total investment to approximately $1,863.The car also received restored headlights, replacement wheels sourced through Facebook Marketplace, and modifications to the exhaust in an attempt to make the V12 sound less restrained. Even after removing resonators and muffler packing, the twin-turbo engine remained surprisingly quiet.Rich estimated that the transmission service parts cost $125, while the fluid added another $68. The replacement wheels cost $400, and the suspension hydraulic fluid added roughly $70 to the final total.Proof That A Proper Diagnosis Is ImportantThe project illustrates why an apparently failed transmission should not always be condemned before proper testing. Low fluid, damaged electrical connectors, failed sensors, and conductor plate faults can produce symptoms that closely resemble severe internal damage.AdvertisementAdvertisementOlder high-performance luxury cars can still be expensive and labor-intensive to repair, especially when several neglected systems fail at once. In this case, careful diagnosis saved a V12 Mercedes from becoming a parts car and turned a seemingly hopeless purchase into a running, driving sedan.If you want more stories like this, follow Guessing Headlights on Yahoo so you don't miss what's coming next.