Unfortunately, galling can take place even on hard anodized parts, especially if accelerated by corrosion. Aluminum doesn't "rust" but that's because "rust" refers only to hydrated oxides of iron. The oxide layer that protects aluminum (and which is artificially thickened and often colored in the anodizing process) can be destroyed very quickly by enough pressure to deform the relatively soft metal under the super-hard but brittle oxide (essentially polycrystalling sapphire), which could occur if the adapter were tightened with grit in the threads; moreso, aluminum oxide and then the metal undeneath will literally dissolve in water with significant chloride ion (like sea water, sweat, etc.), causing corrosion pitting, redeposition, and what amounts to welding.

If David has been at your lens and super-glued the ring in place, you might be able to debond it with acetone (I'd suggest standing the lens, big end up, in a tiny cup of the stuff and checking it every few hours for as much as 2-3 days -- but beware of the flammability of acetone vapor!), but if it's galled or corroded in place, the only solution would be to cut most of the way through the ring (very careful application of a hacksaw or rotary tool with cutting wheel), insert a screwdriver in the cut and twist to break the remaining metal in the threads, and then pry the ring open to get it off the lens threads; more or less like splitting a seized nut off the bolt. This will likely work if it's glued, too, but either way there's a very distinct possibility of completely destroying the rear section of the lens (in case you're not aware, the Spiratone 400/6.3 comes apart at the tripod mounting ring).

Meanwhile, I think I'll pull the T-ring off mine and give it a very light coat of the Superlube Teflon grease I keep around for stuff that needs to stay slick...