....and the results are in; ring has been removed. It might not be pretty, but I was able to break it free this evening with channel-lock pliers.
Before attempting, I unscrewed the junction box assembly from the tray and worked the audio wires a bit so that I could pull the tube out. Then I held the box down firmly on a sheet of rubber gasket material on the edge of the workbench with the rest of the tray laying down next to it; (there was just enough slack in the audio wires running through the tube). It wasn't easy at first, felt like it was held in place with a gummy material but couldn't actually see anything. The more I unscrewed it, the easier it got.
The ring has a fre "extra" grooves in it, but lives to see another day if I should need it again. Perhaps the Evap-O-Rust loosened up the corrosion just enough.
Matt
W2NS