Shimming changes are done at a valve job.

Lifters can be changed without shimming changes. Yes, if they are in your engine-leave them. Inspect rocker arms, camshaft when replacing the lifters.
The decision on to replace all or only a few is subjective and partially mileage driven. If you have one which is colapsed, then just replace it!!
My time is at a premium, so if it was my car it would get a set of lifters. I use Mercedes parts for internal work exclusively! It would have to be a large price difference to consider anything else for me. I've had problems with the others and it's not worth it for internal parts. Never got a bad engine part from mercedes *yet*.


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E