Another possibility is dirt/grime in the pot preventing a full off. You might try one of the Caig cleaners.
Sound when volume off
I have an older preamp but one that I have been happy with for a while. Recently I noticed when I turn the volume all the way off there is still some sound that comes through the speakers. On mute there is silence. Is this a problem? speecifically I thought I once heard that caps might need to be replaced in this situation. All replies are appreciated