[morzh]

Eric.....yeah, man, hate to break it to ya, but as Chick said (and you probably suspected it all along when you said something about "your zeal to free it up") you had likely broken some sort of a tab.
Which considering the degree of seizing (two hands effort and Robo-grip pliers produced little if any movement....what did they use for lube, Liquid Nails?) is something no one should be blamed for.

I do not remember how this thing looked exactly (I liked the idea of it coming out completely when the retention ring was removed...oh, wait....I did not have any retention ring ) but if it had some sort of rib or a peg, you could (now that you can pull it out) in case of a peg drill a little hole (carefully not to break it) and glue in a cylindrical peg of some rigid insulating material, or if it is a a rib, simply glue a small bar of something along where the original was.

If you could produce a photo of what you have and point to the place of where the stop was we could brainstorm it here.
Of course it might be not on the rotor, but on the stator.....same thing, get a photo.