The brief
The C180 had visible oil leaks under it, a burning oil smell, a low oil level and a touch less performance than usual, but a check of the engine bay found nothing weeping up top, none of the usual suspects, the valve cover, the front cover, the sump. He brought it in. When there's an oil leak but nothing visible in the bay, the flywheel oil seal is the prime suspect. That seal, the rear crankshaft seal, sits where the engine meets the gearbox and stops engine oil escaping from the back of the crank. When it hardens and fails, oil weeps out there, tucked between the engine and the gearbox, so it shows up as drips under the car with no obvious source up top. Left long enough it can contaminate the clutch, so it needs proper attention rather than topping up.
The diagnosis
On the lift the leak traced cleanly to the flywheel oil seal, weeping at the back of the engine where the gearbox bolts on, with everything in the bay dry. With a job this involved, confirming the source first matters. That's a seal replacement, and on this car it means dropping the gearbox to reach the flywheel and the seal behind it, then a fresh genuine Mercedes-spec seal in.
The work
The gearbox was supported and dropped, the flywheel came off, and the old rear crankshaft seal removed. The seal seat was cleaned up, a new genuine Mercedes-spec seal fitted carefully so it sat square, the flywheel reinstalled and torqued to spec, and the gearbox bolted back up. The oil that had tracked down was cleaned off and the engine topped to the correct level. A road test followed to confirm it stayed dry and the level held.
The outcome
Dry flywheel area, no oil around the bellhousing, the oil level holding, and no burning smell. The C180 went home with the leak closed off. A flywheel oil seal leak only gets worse, and it's tucked in a place that gets expensive to reach, so doing it properly with the gearbox out, once, sorted it for good.
