I received some salvaged controls courtesy of grimer today. They came well packed in electrolytic peanuts
Unfortunately, this focus control is bad too. Not totally bad though. I get the correct 0 to 1,500 ohms on one leg through the full rotation. The other leg is open so there's probably a break very near that lug.
The original focus control in my 20X12 had failed too! I'm starting to suspect a design flaw
Time to investigate. I carefully popped open the one that originally came with this set by prying back metal tabs. Sure enough - there's a definitely break about 20 turns from one end.
This resistive (nichrome wire?) is a pain to solder so I wedged in a scrap of copper foil plated with gold. It seems to work OK, but there's a noticeable "bump" when the wiper goes over the damaged area. Luckily, this control isn't adjusted much and the damage is near one end.
I'll pop open the one from grimer too and try to repair it. Whichever works better will end up in the set.