The used potentiometer arrived Wednesday. However, the lower carbon track showed a lot of wear:
However, being an optimist, I installed it anyway, hoping for the best. I was able to start the car and get it adjusted to spec, but as expected it did not work well and it caused the check engine light to come on.
Yesterday I found a source for new potentiometers and have one on the way. The seller claims they are after-market and that he had them made, but claims to test them before shipping and he is offering a life-time warranty. I'll make a report once I have it installed.