I am trying to replace the upper seatbelt retractor in my 97 SL2.  It is
hidden behind the trim on the B-post, near the floor.  There is a single
bolt and a cutout key holding it in place.

The bolt is quite large, a T-50 Star head.  I have a hunch that it may
hold more in place than the seatbelt (maybe holds the floor pan to the
frame?)

The problem is that the bolt will not disengage.  It unscrews maybe
three quarters of an inch, but will not come out.  I tried prying it,
both while I was unscrewing it and not, but no luck.  If there is a nut
behind this, I cannot find any holes to access it.

At the end of the throw, it seems to turn about one full turn, then
"clicks" and feels like it is pulling back slightly.

What kind of bolt is this, and what sort of voodoo (or special tools) do
I need to remove it?  Once I have it out, will I be able to replace it
back where it goes?

Thanks for any help

Jim