The brief
The owner had been finding small oil drips under the E200, specifically below the bellhousing where the engine meets the gearbox, and the gearbox itself had started to look greasy on the underside. He brought it in suspecting this was a bigger job than a simple gasket. He was right.
The rear main seal, sometimes called the flywheel oil seal on this engine, is the seal where the back of the crankshaft comes out of the engine block. It keeps engine oil in. When it hardens and fails, oil weeps out the back of the engine and runs down the bellhousing, which is exactly what was dripping. The catch is where it lives: to reach it, the gearbox has to come off the engine.
The diagnosis
On the lift the source was confirmed. The oil was weeping from the back of the engine where the crankshaft exits, then tracking down the bellhousing and dripping off the bottom. There's nothing else back there it could be, that's the rear main seal.
The owner was given the honest choice: a seal that small can sometimes be left to seep and topped up. But the loss rate here was already enough to need regular top-ups, and an oil-soaked bellhousing isn't something to leave. So the proper repair, gearbox out, was the right call, and the kind of job you want to do once.
The work
The gearbox fluid was drained, the drive shafts and propshaft disconnected, the gearbox supported on a transmission jack and separated from the engine. The flywheel came off to reach the rear main seal.
A new Mercedes-spec rear main seal went in, and while everything was open the gearbox-side seal was refreshed too. The flywheel was refitted to torque, the gearbox mated back to the engine with new bellhousing bolts, and the box refilled with the correct ATF spec.
Then a long road test, watching for any drip and checking the level.
The outcome
Dry bellhousing, no drip after a long road test, and the oil level holding.
The E200 went home with the rear main seal sorted properly. On this engine that usually means it's done for the rest of the car's life, which is the right way to think about a gearbox-out job: it's a fair bit of labour, but it's a once-and-done fix, not something you'll be revisiting.
