[morzh]

1. Check if your ground on the vol pot is not done through the case bolted to the chassis, one of the ways it used to be made.
2. Uneven resistance is simple
: the same number of turns but different diameter (an outer turn is longer than the inner; hence the higher resistance).
For replacement, look at the Hammond 125 series; pick one suitable by the size and power. Make sire it is 125, nogt 125SE (for Single-ended).