I posted this before ... but with my '91 300E with 180k miles it was using 1 qt in about 1,000 miles.
I decided to try Valvoline's MaxLife oil ... oil consumption was reduced to about a quart in 2,000 miles.
The last oil change I used the Castrol GTX high mileage oil, a 10w40 and I am still waiting to add oil and I am approaching 3,000 miles.
An oil change is a lot less expensive than valve stem seals.
Try it. Not only are the valve stem seals "treated" but so is every other gasket that touches oil.
I was dubious at first about these "snake oil additives" but now I am sold.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)