I just got a 1992 400e and noticed after my oil change, 1/2 quart is missing in 500 miles. I checked all the plugs. the first 2 plugs on the passanger side towards radiator have a little oil on them at the threads. The tip is dry. I assume that is the famous donut washer replacement. I did not see any leaks. The car has 162,000 miles and I doubt the valve seals were ever done. I am not sure if there is anyway of finding out either. I don't get the ticking noise from the valve guides either. Where is my oil going?