Success! The After hosing down the inside with PB Blaster from the back and the bottom of the pillar, a few minutes with the hair dryer, and a few more minutes of rocking everything with a padded lockjaw, I finally got it to turn. It now spins fairly freely. While it sits a bit more, I'll start on polishing the rest of the parts. The head unit and front tension disc will be last, so I can keep track of what goes where.
Does the PB Blaster need rinsed off with kerosene or something, or will it evaporate on its own?