[James]

I am not sure how you sprayed the control, if you were able to actually
access the inside of the head unit or not.

On one occasion, I was able to take the radio out of the car, and hold it up
vertically so that the vol control shaft is vertical, and spray cleaner on
the shaft itself, and eventually it ran down into the pot and cleaned it !!
So, I was able to fix the pot without going into the inside of the radio.

But, it appears that at least, you have probably isolated your problem.

Good luck !!

James