[Thomas.Schumacher]

Just in case you have not checked it directly, the cam cover on the older diesels, tends to leak just enough to make it look like black oil is coming out of every possible place. It will leak at the very back of the cover. Replacing the gasket will help for a while, but the real fix is to removed the cover, clean it thoroughly, the examine the area inside and around the lip. I have owned three of these engines, two turbo and one not, but all three leaked. A central American mechanic showed me how to check and grind the slight rise that causes the leak. Find a mechanic over 50, with a name like Crusty or Bud, who knows Mercedes engines. He will know what to do. Very small operation.

As Harald notes, the rear main can leak, although I have never had one fail. But, when it is bad enough it is a big job. If you have a clutch-manual transmission, this becomes more necessary to fix as the clutch is not noted for its ability to operate as an "oil bath" clutch. You can also check for leakage if you have a clutch, by opening the bolt drain at the very bottom of the bell-housing. If a lot of black diesel engine oil runs out, your rear main seal is toast. I doubt if the auto transmission has this feature - since it is a G only feature, and I have never looked at an auto transmission G. Early synthenic oils seem to leak more than regular oil, although I have read lately that even synethic oils now have additives to slow cohesive capillary action...escape. So, if your G rear main is leaking a little, you might try a little heavier oil. I tend to run 15-40 or 50, although the climiate here is mild and I have a building and blockheater for my G.

Good luck.