I thought I'd post this in case it helped others. When your rear seat belts give up the ghost, you can use use the rear seat belts from a Discovery as a replacement. Will Tillery will sell them to you cheap and ship them fast too.
But you might run into a few issues like I did.
1. They are not black like the front belts. Solution - deal with it woosie boy!
2. The "Y" piece is shorter than the old one. Solution - depending on the damage to yours, renew the broken bits from the donor seatbelt system, or if yours are beyond repair, use the one from the disco and teach your kids how to hold them from behind the seat as they buckle
3. This one is a biggie. Either the belt is shorter or the distance from the reel to the top guide is longer than on the disco, but regardless, the net effect is that if you retract the belt fully to the locking position (where it will just ratchet back in before allowing to be reeled out again), it cannot retract far enough back in to release. If you think this is unlikely to happen to you, just throw 2 kids in the back seat and wait about 2 minutes. Solution - make an extender to lower the top guide piece. It doesn't take much. Mine lowered the guide 2.25" and that was sufficient. The extender is just a piece of steel plate, with 2 holes 2.25" apart on center. The top hole is 9/16" and the bottom 1/2". I used 1/4" steel plate as it was free (thanks Tony!) but it's overkill - the other stock parts of the system are half that thick.
Attached are pictures of the extender (drying after a quick coat of paint), and then installed.