Rear main is inside the bell housing.

I suspect you have a leaking oil gallery plug. Probably have to pull the engine to fix, it's a hard steel ball driven into the block.

Peter

__________________
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!