I thought squelch was a knob on the unit that you adjusted up or down to reduce static and/or low transmissions. Never heard of a spray on or brush on deal...seems weird to me.
Sounds like maybe a circuit is broken, or maybe you just need to put some contact cleaner on it.
I know on some old marine radios on the houseboat, after sitting unused all winter, you had to turn the knobs up and down several times to clean the contacts before they would work right for the rest of the summer. Never had to use any contact cleaner by just doing that.