The oil filter housing gasket can leak on these cars, too, running oil down the rear of the block. I'd fix that before going after the rear main.

Best thing to do is to pressure wash the engine carefully to remove all the old oil, then spray it down with foot powder. This will coat the engine with white powder -- black oil leaks will be VERY obvious.

Run it for a while and see where the black show up.

A rear main leak will only put oil on the tranny and back -- if the engine pan has oil on it, most likely you have a leak somewhere else.

Slow, noisy starts and smoke at idle warm with good compression make me think of a worn timing chain and hence late valve and injection timing.

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!