I have some minor leaks on the 300D -- worst one was a leaking oil
filler cap, replaced them on all the Benzes and reduced the oil
consumption considerably. I never have to add oil between changes
(6000 miles or so) on the 300D, have to add a quart or two on the TE.
The 220D, when running, uses at least a couple quarts to a tank of
fuel, so I ignore leaks on that one!
Check the oil filler cap for leaks -- remove cap, wipe area completely
dry, and re-install cap. The presence of ANY oil around the cap after
driving indicates it's leaking, replace.
Peter