Two most likely culprits at this age are the front crank seal and the valve cover gasket. The valve cover gasket in particular will allow oil to run down the engine and off the back.

On the 616, a leaking oil filter housing will also look like a rear main leak.

A leaking o-ring on the separator return line from the air filter housing, or a leaking separator will dump lots of oil, too. A clogged return line will dump it down the intake.

Any of these can dump a couple quarts to a tank of fuel on the ground -- if you are getting oil drops under the car, you need to find and repair the leak.

Bad valve guides or guide seals will cause serious oil consumption too. Blue smoke on startup or on decelerations is a clue here.

Oil consumption doesn't suddenly skyrocket unless you seriously overheat the engine.

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!