Is it an older style potentiometer (variable resistor)? Regardless - most 'controls' for volume and other functions can be pretty compact and don't lend themselves to repair. The larger old pots could be opened and inspected - increasing the likelihood of making a repair. I presume that you've measured it to determine that it's shorted. Did you make the right measurement? Did you adjust it -take it thru it's range just to be sure you weren't seeing the value at one extreme of rotational or linear movement.