300SE Oil Consumption

[TClanton]

My parents have a 90 300SE that is using approximately 1 qt of oil every 400-500 miles. They just had new valve seals installed and are using 10W40 oil, but haven't seen a reduction in oil consumption. We have searched the archives for old posts and excessive oil consumption seems to be a recurring problem for these cars, but we aren't sure what to look for next or if anything else can be done. There do not seem to be any leaks...never any oil on the ground and the motor is dry and clean. There is no smoke on starting or during acceleration.

The mechanic did not do a complete valve job when replacing the seals, but indicated that the existing seals were not even in bad condition. This car has only 80K, runs great and has a great service history....what should we be looking at next? Any suggestions? Even my old diesel doesn't burn oil like this thing.....:p