I have ventured over from the diesel section....

My brother has an '89 420sel with 240K miles on it. His mechanic (not me)said that two cylinders were leaking oil past the rings and fouling out the plugs AND that a rebuild was in order. I come from the diesel world so a MB engine with 240k on does not sound like it needs rebuilt. The car runs very well but smokes ever so slightly from a stop light in the summer.

Should I dump some marvel mystery oil through the plug hole and let it soak? We think the car has sat for a long time... so I think the rings are stuck.
If the rings are junk should we try to put new rings in?

He hate's the idea of junking the otherwise nice car because of some fouling spark plugs.

Thanks

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D