I too have restored a "broken" window by sinply cleaning the switch. A pencil eraser will get off the grime and corrosion, but leave the plating intact. Then, I just spritz it with some contact cleaner and put it back together.

Our diesels are between 20 and 40 years old - who wouldn't expect a little buildup? The next time I buy an old Benz, I will be doing this procedure to all the switches in the car. It's basically free, if you already have the pencil and contact cleaner.