Most likely they can be cleaned/restored to proper condition with any of several different cleaners UNLESS they have actually disintegrated internally. I do a lot of vacuum tube equipment restoration and scratchy/noisy/siezed volume pots are pretty common in equipment that been sitting in a basement/garage and hasn't been used in 40, 50, or more (sometimes a LOT more) years.
WD 40 works fine though purpose-made products like DeOxit are very popular. IMO, the best thing is CorrosionX. One method that works very well for a long, trouble-free operation of such old controls is a thorough spray with the cleaner into the control(s) and, after it is working properly, pack the control's internals with silicone grease (di-electric grease).
You just spray the cleaner into the pot and then turn the knob back/forth through its full travel. Repeat until the scratchiness/ random operation disappears. In the case of a seized control, let the cleaner sit for a bit and then try to work the knob. Don't use excessive force just move it back/forth slightly. As the cleaner does the job, the internal corrosion that is causing it will break loose.
Hold the control so that the cleaner can drain out for the final spraying. Continue to rotate the knob a few times after the excess cleaner drains. Then try to work the silicone grease into the control. This may or may not be very easy to do. Corrosion X is good because it provides lubrication and protection but silicone grease is better if you can get it in there.
Most volume pots can be disassembled but that usually isn't necessary.
