Remote volume out on TAD-150 preamp..options?

I have a TAD (Tube Audio Design) 150 preamp, designed/built by Paul Gryzbek.  The preamp was quite poplar here maybe 15-20ish years back.  My remote volume went out.  The remote works, but the volume pot in the preamp no longer responds.  Sadly, Paul passed away a number of years ago.  I had a local audio repair guy look at it and he said it's beyond his understanding. 

Any ideas who/where it could be fixed?   I'm in SE WI.