As spraying Contact Cleaner only fixes the issue for a month or so for me, I went in with a Multimeter, and figured out how to just bypass the switch altogether. Makes your ‘selection’ permanent, but not a big deal for keeping the speakers out of the trash. I clumsily wrote my first guide ever on how to do it yourself, hope this helps others: Mackie CR3 CR4 Links/Rechts Wahlschalter überbrücken Labeled ‘difficult’ because it requires soldering, but if you are comfortable with that, this is a quick and easy fix.