The best thing any guitarist can do is to go to radio shack or its international equivilent and buy a $10 digital multi meter. One that is capable of reading:Resistance, Capacitance, Transistor, Diodes and Volts is all you need. They come with a instruction book to teach you how to use them BTW and are very simple things to use.

Then you can check parts to see if the part in question is indeed the part with an issue. But it probably is a broken/breaking pot.

http://www.mouser.com/ sell them but things are almost impossible to find on mouser without downloading their catalog and finding part numbers or being familiar with parts variables. I don’t have a direct link to them on mouser, you’ll have to search for 24mm split shaft 100k Linear PCB mount long pin pots.

You can just buy this pot http://www.smallbearelec.com/Detail.bok?no=710 and make the knob fit by enlarging the hole in the knob. it can be done.

Or alternatively you can email info@ehx.com and ask them to send one out to you, they may, especially if its still under warranty.

If you have no luck with any of this, report back here and I, or Ron (an EHX genius), will try help some more.

the best advise i could give is to listen to Liberty Belle and EH-MAN, i would also like to add that it may be bad solder connections to the pot in question, or the pot itself may be able to be fixed yourself, by removing the metal tabs that hold it togeather, and using an electronics or pot cleaner on the inside, and/or bending the slider to properly have friction on the plate.