Bob,

The entire chamber housing the circuitry is potted with black epoxy.
I'm dremelling in where the potting is up against the wall of the
speaker where the pin inserts. It appears that the pin has broken off
inside of the wall of the speaker and extends a way into the potting.
I'll know more when I get a stock post to compare it to.

I've found the post (the sparks gave it away) and now I'm going to
dremel around it and pick away carefully using something like a dental
tool.