I wish I could find a shop that rebuilt them. Too much liability I suppose.
My understanding is that belts before a certain year behave differently than new belts. If you tug on a new belt hard, it locks almost instantly. Only belts don't seem to do that and rely on inertia to trigger the locking mechanism. Not 100% sure. The pre-90 or pre-91 belts have a tensioner in the door. It's the black plunger under the door latch. It connects to the seat belts.