It appears that I have the same mechanical encoder problem that has caused the volume control knob to fail on my home theater receiver. I think I have located the replacement part at digikey. I cleaned the encoder and it got a little better. Then I tried bending the tang that contacts the encoder and ruined it. Now I have ordered the part in the link below.
https://www.digikey.com/products/en?keywords=PEC16-4020F-N0024
Bourns
PEC16-4020F-N0024
https://www.digikey.com/products/en?keywords=PEC16-4020F-N0024
Bourns
PEC16-4020F-N0024