My '92 300E, same engine as yours, has a slight head gasket leak. Has had it for 100K miles more or less. Car currently has 233K and runs fine with no oil in the coolant.

Quote from my indy is 1200 to 1500 dollars for valve job and , of course, new head gasket.

I it was me, I would want crawl under there and look closely for the leak. From what I have read the leak on this engine is normally passenger side toward the rear of the head. That's where mine is. Could it be that your leak is actually from the front timing cover? This is also common.

Steve