Here is what I did for the repair. The suggestion of JB Weld looked good, but I decided to have another go using cyanoacrylate (this time Gorilla Super Glue) and a different approach. When I was talking to the glue guy in the local hardware store, he asked if there was room to cement some kind of reinforcement across the crack. I said no, but then starting thinking about it. I wound up filing/grinding down sections on the disk to make room for reinforcement, glueing strips of plastic (mostly bits I cut from a separating strip from a parts organizer drawer), and then filing/grinding those down so the repaired disk would fit and turn easily inside the volume control housing. Worked great, and once again the old Dynaco amp is pounding bass out through a matched set of Dynaco speakers. Thanks John and Dan for your input. I’ll attach a pic of the repaired shaft, so you can see what I was describing.
Don
