If found that spraying a little CRC battery protector into the cap and then applying it lightly with a q-tip to be an excellent way to prevent corrosion @ exposed contact points.

Also, make sure that the contacts aren't just cleaned, but are bare copper. Sometimes you can get a little carbon build-up that a chemical cleaner can't remove, so a little manual work is required.

Have you checked the usual suspects? Loose/weak grounds and the like? I've seen more than my fair share of phantom issues caused by a bad ground. What about the idle control or the contacts to the ECM (or whatever MB calls it)?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.