Well from my experience, I can be sure of one thing, it don't need rings. If it is using oil it is through the valve guides/seals or leaking 100% of the time.

Any tech suggesting rings are the problem on that car with those symptoms doesn't work on Mercedes on a regular basis. Thats what we call a roll the dice technician. if you start by replacing everything under the hood maybe it will work right after you get a tech that knows what he is doing to set it up properly. I'd just start with that tech first.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician