I have a new (to me) 1990 300E with only 91,000 miles. Had the oil changed at 89,000 and had the car checked out. I checked the oil yesterday and it was 2 quarts low. I see no leaks on the garage floor or anywhere in the engine bay. The oil was changed by a very good MB mechanic so i expect he put in the right amount. Is it normal to burn 1 quart every 1000 miles? Ideas?