I'd try squirting a shot of WD-40 into the slot behind the offending knob...if you can get the liquid into the switch, it'll likely make the switch work for a while. I somehow got an extra year or so out of a seat switch that way.

Good luck!

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo