Before you replace the switch assembly, go to Radio Shack and get a spray can of their electronics cleaner. I don't remember the name of the product, but it is a cleaner/solvent that works on switchgear and circuits. I have used it successfully on my window controllers in the '98 E320.

Best,
g

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64 230sl, my daily driver
94 E500, sold
98 E320, family and dog hauler
04 C240, safe machine for teen drivers, but a poc
08 audi a4, yes we have gone to the dark side