my 1985 500sel runs aobut a mile more on a gallon with 93 octan than 89 and my mannual says min. octan 97 should this matter and what kind of damage would 190k on 87 do to my engine.

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1985 500sel 220k
1981 300sd 278k sold
1989 chrysler
leabaron 130k
1990 380sl (hopefully)