First of all $800 sounds very reasonable for a valve job on one of these cars. Ensure that they are replacing the guides for this price.

Secondly, if it were me, with this high mileage engine, I would do a compression check, record the numbers and check compression again after squirting oil in the hole before putting in the compression guage. This will show if there is any compression loss past the rings. If the rings are tired, and the valves need grinding, the additional compression from the fresh valve job will possibly push more oil past the rings.

The infamous valve seal problem on these engines was corrected in the early portion of the engines life by changing valve seal types. Since you did not buy the car new, and it sounds like you don't know the engine history, the seals were PROBABLY replaced previously. Replacing them would be a "pig and a poke".

i'm glad you're enjoying your 124. There are plenty of relatively low mileage well cared for examples available right now. Maybe it is time to think about finding another. One quart in 1,000 miles is not so bad that the car has no value.

Best of luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles