Hi John, I'm Carl and welcome to Just Answer. If you have to mess with the Treble Potentiometer just to get sound then the Resistive Contacts have some sort of insulative coating over it. You'll need a can of contact cleaner or rubbing alcohol to spray in there while turning it back and forth in order to clean the contacts. Take a can of compressed air to dry it out before turning back on or wait 30 minutes to air dry. This should have you back up in going again!
If you need any clarification or have any additional questions, please feel free to ask me.