First, fix the wiring. If one wire's busted, then two/three could be about to fall off.
Then, clean the pots. First, just turn 'em back & forth like a few dozen times each to see if that clears the crud off the resistive element.
If not, consider giving each a blast of Caif DeoxIT, then repeating the previous step.
If that doesn't work, then measure resistance with a $10 VOM, or just read what's stamped on the pot's shell. Seems like 250K is pretty much the standard for passive bass circuitry, & there's no good reason to pay more than $7.95 (Musician's Friend). Get linear taper, of course.