300E valve stem seals and oil burning

[dacia]

The car is an '86 300E with about 250K miles on it. It is burning about 3 quarts of oil per 3000 miles (I am not the first owner, I wish I was). Talked to my Benz Pro, quoted me $800.00 US for a head job or $200US for changing the seals only. My question is how much of an improvement could I expect in oil consumption from changing the seals only as oppose to going for the full headjob?
By the way the car does not smoke not even at start-up so I am wondering where does the oil go? It is not in the coolant, not under the car so I guess it is in the catalic converter? I am not planning to keep the car for many years to come meaning don't really want to invest into that headjob unless absolutely necessary. And yes, I will buy another 124. Best car I ever had!
Thanks
Alex