Looks like a test point to me. I will quit fretting over it. The schematic shows their 3-position range switch in the same neighborhood, so perhaps my local/distance guess wasn't completely insane.
Unfortunately, the green glow seems to be gone for good, no matter where you put the ion trap. It was fun to see, anyhow, even it seems a little gimmicky. I can see using it for a coarse setting, but I'd want to make the final adjustment looking at the screen.
The CRT is indeed a Rauland and its label has some instructions about using the green marker. Sooner or later, I'll loosen the retaining strap so that I can read the whole thing.
The tuner appears to have two strips per channel; it looks like the one in my Admiral console.
Thanks for the other advice. I'll check out that replacement resistor (and the replacement caps, for that matter).
Regards,
Phil Nelson