Hi @Witch and welcome to the forum!
It appears that you have conducted thorough testing. It seems pretty watertight that the switch is the issue. But would you please take a look at this “no sound” checklist (skip any ideas you have already done)? It might help catch any issues before attempting a repair.
A good way of testing the circuit is toggling from BYPASS to OPERATE. If both positions have the problem, then the issue is indeed very likely the switch. Typically moving the switch up and down can help clean the contact. You have done one step beyond this with the cleaner.
I believe that switch is a custom part, so a replacement would need to be sent out to you.