If the plugs are clean, as they probably are, replace the oil filler cap and valve cover gasket before getting too excited.

The cap will ONLY leak at speed, when oil is thrown off the cam onto it, it won't leak idling or in town. Clue is that there is always oil around the filler cap even if you wipe it dry carefully betweel fills. The oil will run down the head and off the rear of the engine, and since there is so much, and it's hot, it won't collect the black crusty stuff a typical leak does.

If you smell burning oil occasionally, the valve cover gasket is leaking all round, too, replace.

Front cam cover seal is also a known leak on these cars, but that usually causes oil to run of the oil pan. Not always, though -- that sound panel under there holds quite a bit.

If the plugs are crusty, time of a valve job.

A quart in 700 miles with bad guides would be obvious from the blue smoke on startup and after sitting at lights.

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!