My 1988 300ce began burning oil at a rate of a quart every 1,000 miles or so about a year ago and progressively got worse..down to about one every 400-500 miles. When I had the 52,500 service done 4/03, the MB service rep asked me if I was burning oil. Told yes, he said I probably needed valve seals.
Had the job done at 57,900 by an indy in July.. Parts: Seals = 31.00, valve cover gasket = 17.50. Labor (4.2 hrs) 361.20.
Had the 60,000 service done by MB two weeks ago. During that period, no noticeable oil consumption. Problem solved.
I guess this shows that seal deterioration and failure can be a function of age as well as use.
I didn't catch the mileage on your 87 300e, but if it's not too high, you may solve the problem with just doing the seals.