Get some electric contact cleaner and spray into the holes once the switch knobs have been removed carefully. That should temporarily get the rear part of the bottom cushion to lower.
Then when you have time take the switch out and clean it thoroughly.
During installation once everything is cleaned, apply some die electric grease.
http://www.benzworld.org/forums/w201-190-class/1476077-electric-switch-cleaning-lube.html
