I have replaced a few of the rear main seals in the 104 engine, however, I would not think it would leak that badly unless it was installed incorrectly. ON a sedan, the labor time is around 8-10 hours I think. The G will be more because of the transfer case and 4 wheel drive.
Be sure to have the head gasket checked before doing this, the head gasket is the most common of oil leaks for this enigne.
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MERCEDES SPECIALIST 11 YRS