You can easily remove the knob from the stiff encoder, pinch it and firmly (but not violently) pull up and the encoder knob will slide off. Use your phone flashlight or some other bright light and shine it around until you can see into the hole surrounding the E encoder. If it looks like there is any kind of hair or lint, something wrapped around it, you may need to take it apart and remove the obstruction.
If the encoder itself has become immobilized internally, it might need replacement. You could try using a specialized lubricant but it’s not guaranteed to help, cheap to try though. If you want to do that I would probably recommend using deoxit fader lube as at worst it will be harmless, don’t try using contact cleaner spray on the encoder as I think this would be more harmful than good.
I have used this and know it is safe, also inexpensive. F100L-L2C
Don’t use too much, just a little bit should help. After applying to the encoder’s shaft (right where the shaft meets the bushing) rotate back and forth in full rotations and let it penetrate, see if it helps. It will not help if there is an obstruction such as hair wrapped around the encoder, you’d need to disassemble and remove the obstruction if that’s the case (as stated previously).
The volume knob wobble is either going to be because the shaft is loose, or the body of the potentiometer is loose. If the shaft is loose, someone may have tried to clean it with contact cleaner and now it has none of the insulating grease left, if that’s the case eventually it will probably fail.
If the body of the pot is loose that probably means that the metal housing which has the bushing and retains the lower plastic part of the pot body has come loose. There may be a way to carefully crimp them back together with a set of pliers (where the little claws from the metal housing grip the pot body) or to add a blob of solder to secure the connection but if you don’t have a lot of electronics repair experience you may just want to use it carefully from now on.
As far as support, I don’t know what to tell you. They may be busy and still respond, but if the mfgdt is in 2020 the warranty has already expired, you would definitely pay for shipping and repair. May be less expensive to have it repaired locally.
I’d start with observation and the $5 tube of deoxit, make sure you get the one I showed you because there is another one which is similar to contact cleaner and you want to clean and lubricate, not to flush out the existing grease.
The encoder has a D shape to the shaft, when you put the knob back on, make sure the flat inclusion lines up with the flat part of the shaft.