Well, it's good to know that it's not unusual for threads to be showing, but I tried turning that thing with a 3/8 ratchet with a aluminum tube on the handle and I couldn't get it to move at all, in fact, it started to strip the allen head on the bolt/plug.
I suppose it's possible that I just didn't have it lined up straight as that bolt is on a diagonal axis and I'm coming at it from the top...
I'll try letting some penetrating oil soak on it for awhile and see if that helps.
If not, I suppose I'll be drilling that little sucker out.
<in Homer Simpson voice> WooHoo!