I have a C-20 with a similar problem, except my L-R balance is always terrible. (Instead of pointing my balance control straight up toward the 12:00 position, I have to point it to about 2:00 - 2:30). I have also had it in a few times and have had the caps and a few other parts upgraded. But the L-R balance is still way off.
I also suspect it is the volume control and have made arrangements to have a new, upgraded volume control installed. I don't know if they make upgraded volume controls for the C-22 but I could ask while my C-20 is in for the service.
I'm scheduled to have the service work done later this month or early October (depending on how fast work gets done on current projects).
If you like, I can keep you posted of my results, and inquire about your C-22 as well.
PS If you decide it's the volume control and live near Chicago, I can tell you where NOT to go.