This is such a great unit, so well designed and built.  The owner mentioned the input pot was not working. The unit arrived with what looks like impact or shipping damage.  The left corner of the front panel place was bent slightly back.  On inspection I found the input pot sheared off.

I found the  sheared input pot first...

Then I noticed the bent front panel...

I took the face plate off and carefully bent it back in the vice.  I was worried about further damaging the front paint job.  I don't think I got it completely straight, but I got is close as I was comfortable with.

I put in a temporary pot in and unit started to pass audio again. 

I then set out to recap all the electrolytic caps.  This unit was stock and the caps were put in 1981 I believe.  They all still functioned but there was some with a higher ESR.

I also looked the op-amps.  The input became cleaner and seemed to have a slightly lower frequency response with a 5532 in the front end.