I'm having a similar problem, I bought a used 404, the volume is stuck midway, only audio through right channel. The volume pot seems looser than the other three knobs. Wondering if the pot itself is shot. Anyone know where to get a replacement?

I've got the same problem with my 404, tried re-soldering the volume pot and one of the broken FX pots, but made no difference. You can only get the replacement pots through Roland, who have to order them from Japan. Costs about £30 with the shipping for the 4 knobs