Can't tell about getting to the switch... was easy on my W126 ... if I remember correctly, just unscrew side pieces and ease it out ... careful, don't crack it - is easy to do and are expensive.
Rear window switch is least used, right? Try taking it apart and cleaning and then a tiny bit of light lube. I did a front ... was getting ready to go buy one and then popped it apart - LOTS of pieces ... seems like a spring, couple of clip pieces, a ball bearing or two ... and then I swapped it with arear ... works fine.
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg