There are several things that can leak on the front of the 617 engines:

Large bolt with aluminum washer seal next to the timing pointer (covers a bolt pin for the slide rails, I think).

Several bolts that hold the power steering pump in place -- they go into the oil space and must be sealed with Permatex when installed, or they leak.

Vacuum pump housing at the bottom -- hard to get to this bolt on W115s, easier on W123s.

Font seal.

If the front seal is leaking, it will throw oil up the side of the motor in the direction of rotation. Makes a huge mess.

Larry's directions are excellent -- I will only add that the seal actually runs on a spacer, about 6 mm thick -- if the seal is leaking, pull this and reverse it, and if it has a worn spot on both sides, replace it.

Unfortunately, a special puller is required most times to get the spacer out -- it gets rather stuck with time, and there isn't much room. It's fairly important to have a fresh seal surface, as the old rough one will eat another seal in short order.

There is also an installation tool that is very handy for getting the seal over the spacer without cutting the sealing lip. Probably not worth purchase, but if you can borrow one, it will make the job easier.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!