I don't think he handled it too badly.
Shosource didn't like being told their stuff doesn't fit and our poster didn't like being told that....all sales are final. Kind of a draw.
The one thing I learned was: if Sho4life is right that repairing your own mount is not too nasty, then that is a better solution than buying a reworked one.
The OP said the old mount went in and out with no difficulty. That I like.
Everyone seems to imply that this is one hard job to get right.
I am not in a big hurry to buy a reworked one if this situation awaits me.
Next time around, I am going to try to fix my old mount (if time allows).
Who knows, 1989 was a long time ago. Maybe some manufacturers tried making this mount, did a bad job, bailed, and now these things are the cores we are trying to work with. At least you know the one that is in there already.... fits.