It might just be easier to pick up a used one at a local yard. Of course, the yards near you are probably a little cold and snowy this time of year.
I am not aware of any way to get inside and repair your year seat belt latch. Have you tried using a flashlight to look inside and see if something might just have fallen in there and is jammed or if something is broken? With the years on yours, it may just be worn or gummed up. It should be safe to try WD40 to try and clean it out.
On the other hand, if it'* a mechanical issue and it'* just barely catching now, maybe lubing it would be a bad idea...lol.
It really depends on what, if anything you can see using a bright flashlight shone in there. Then maybe instead of WD40, you could use a non-lubricating spray cleanser.
Mike: 1997 SE w/ 183K, aka White Horse
, Gutted Airbox w/K&N, drilled 180* t-stat, tint all around, clear corners w/SilverStars, "PONTIAC" light up tail, PEMs, NGK TR55s