| Looks like 50 Kohms with the "15A" resistance taper. Very common.
But the trick will be finding one with the exact physical dimensions so it can take the place of the old one AND line up with the panel hole -- without hacking up the PCB. You may have to spend some time at Digi-Key or Allied looking at various pots' physical specs. Those big supply houses tend to have great documentation, often with links back to the manufacturers' doc sets. Dreary work but it'll pay off in the long run.
Maybe someone here already knows of a direct (identically dimensioned) "street" replacement. | 
