amplifier imbalance

[Refugee]

I would first swap the speaker leads over to make sure it really is the amplifier. I was once asked to rebuild the cross overs in the speakers after the owner had done the lead swap. We swapped the speakers over and the problem stayed with the speaker location. It was a room layout issue and nothing to do with the amp or speakers.
The crackly volume control is most likely to be coupling capacitors either side of the control especially anode to control. Do the one on the control grid of the output valve while you are at it.
A bad case can burn out the track on the pot.