The depth of siliconizing is enough for one .50mm oversize. It takes special boring equiptment and procedures. MB used to recommend two machine shops in the US. One was in Orlando. I don't remember their name. I have had two done by Bieker Engineering in Burbank Ca. They are mainly a Porsche engine shop but the 928/944 blocks were similar.

I have heard of people sleeving the blocks but I have never read a MB procedure for it.

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