#2
More details about the guitar? Is it a 250k or 500k pot? What are the settings on the amp?
#3
Why dont you start by opening it up and looking to see if there are any loose connections, wires off, bad/cracked solder points, etc....

If everything is well, i would just replace that particular pot. Its like 3 bucks, and easy to change.
RIG
Jackson SL3 Soloist
89' Ibanez RG570
Vader 4x12 Cabinet
Line 6 HD147 Head
6space HEAD/RACK case
Korg DTR1000 Rack Tuner
Furman Power Conditioner
ISP Decimator