Since the pot is really an adjustable voltage divider, you could measure the resistances at various points of the pot's travel, calculate the voltage divider ratio and then convert into decibels. With that, you could then decide whether the imbalance is acceptable.
Ratio = (R1 / R2) + 1
R1 is the resistance between the input and wiper pins of the pot
R2 is the resistance between the wiper and ground pins of the pot