Nick
My car is a 300TE from 1992. At 85'000 miles the head gasket and valve were done. However it always consumed about 1 quart in 3000 miles, running 0w-40 Mobil1. When doing oil changes I added the 6 liters as stated in the owner's manual.
Recently I switched to 15w-50 Mobil EP. Also I only added 6 quarts (instead of 6 liters) at the oil change. The dipstick indicates 2/3 between min and max. Oil consumption has stopped. I do not know which of the two changes caused the stop - my guess would be only adding 6 quarts did it.
Regards, Bruno

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1992 300TE 160 kmiles