[Winky Dink]

A quick update on this. I wouldn't want someone in the future to follow the previous advice in this thread and run into the long-term failure that I had.

Over a period of months, the rheostat resistance continued to decrease. After a year it was hopeless--full volume at the lowest setting. Either the Slip-Plate continued to lose volatile components or the graphite was burnished and condensed where the sweep contacted the surface.

I decided to try plain graphite mixed with epoxy cement. I used the tiniest amount of epoxy that allow me to make a paste with graphite and applied it to a fresh piece of card stock cut in the proper shape to fit the rheostat. After many trials I found a mix that would give me a smooth increase in volume--but in only one third of the rheostat's normal rotation to reach max volume. That was good enough for me.

It's been almost two years since I did that, and it's still stable. The radio is only used about once a week, so in the very long term the rheostat could still fail. I'll let you know how it works five years from now, so stay healthy.