1st how do know it's a short?
Most electronics after sitting unused for many years get alot of dust and condensation build up in control pots which either causes them not to function correctly or even in some cases not at all. There are 2 ways to go about this the easier way is to take bbx apart and use deoxit on all switches and control pots by squirting a little onside of switch/ pot and moving the switch or knob back and forth to clean pots. The other way, and I only suggest this method if you no what your doing is to take the switch and pots apart to manually clean it.
if you are in the states radio shack carries the cleaner as a spray
good luck