My switch eventually completely broke last year. It was increasingly difficult to rotate for a few months and I could hear the insides making noise when I rotated it. When I finally replaced it, I took the old switch apart and found that the ceramic housing inside the switch had deteriorated and the pieces had become wedged between the rotating parts. If you shake your switch and hear noise inside that sounds like a set of maracas, that's probably what it is. The switch itself is an engineering masterpiece. I was impressed. I think it cost about $50 for a new one.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles