I've read elsewhere that the valve stem seals/guides were updated in 1990. For what it's worth, I own a '91 300-SEL(M103) and it uses more oil than all of my other cars(3 Japanses) use. The spark plugs are dry, but I have leakage out the front of the engine. In this area, there are 3-4 places where oil can leak. Bottom line....most M103 motors are going to either LEAK or DIGEST oil. My 2 cents.