Yamaha CR 820 Dang Strange Issue

[Keneye]

Couple of years ago bought a Yamaha CR 820 with a dead channel off of eBay. Finally fished it out. With mute off I lose stereo. With mute in I get stereo. ??? I replaced all the caps except the main caps and the hard to get to tone board. Several videos suggested small value caps prone to failure. I don't listen to AM but if I select it I only get a high pitched whine.
With the mute on and volume up it sounds fine. But why would muting fix the stereo issue? Meters work as well as stereo indicator light.

 

[avionic]

Dirty MUTE switch..

 

[avionic]

I don't listen to AM but if I select it I only get a high pitched whine.

Just don't listen to it.

 

[Keneye]

Just don't listen to it.

Doc it hurts when I do this. Then don't do that!

 

[Keneye]

Dirty MUTE switch..

Used Fader lube. Plan to remove it and check it's operation. Wondering if it could have been wired backwards from the factory or at some point.