Put a new wiper lug on the horizontal centering pot, then reassembled and reinstalled both the horizontal and the vertical pots. Checked that there were no shorts between the wipers and the other terminals. Hoped that this would somehow cure the horizontal frequency problem, but no-o-o-o! And then I checked the pot cases and found that they're still hot. Bummer! I assume the metal cases should shoot sparks when they're grounded, but I can't find anything wrong with the circuitry.
Other than retracing all the circuits for the fortieth time, I'll try switching out one or more of the presumed-good mica caps. I don't have the parts for that yet, but I expect the dog sled from Just Radios to arrive any day now.
- Winky