Thanks, @chines1 for the useful lesson.
So now it appears what maybe happened is the Bakelite disintegrated—or the Micarta replacements did.
Presumably I've got the same in all four corners which means I'm back to the Delrin stuff if I don't want to use the sand rail solution (Sorry, @Gordon Nichols, I don't. I actually bought and then, after reading up on them, gave away a set of those urethane sleeves years ago.)
It would have been really helpful for Cip1 to include a note on the page with those inner bushings, to the effect of, "Caution, you must use the correct bushing carriers for these, NLA."
I love to waste $80 plus two weeks.