The organ is a Hammond, model number H 182 built in the late 60's or early 70's. There are no capacitors.
This morning the pedal sustain does not fade at all indicating that the condition is now permanent. I think you are right about it being a tube as there are no other electronics. If I knew which tube it was and had one, I could fix it myself.
I think we have done all we can on this matter at this time. "opening it up" is not something done easily any more as I'm an old man and need help to lift it away from the wall. So this process will take some time. I have a possible source for a service manual and possibly some tubes that I will pursue. Thanks for your time and trouble.