How to fix a stuck seat belt VW GTI 2009

I just solved the problem for a stuck rear center seat belt in my 2002 Jetta.

Flip the base seat cushion forward against the front seat backs. Trace down along the belt to its tether point on the floor. The belt is sewn around a steel loop. The loop is anchored to a black steel hook. A thin silvery retainer plate is spring tensioned on top of the loop to prevent it from sliding off of the hook when the seat back is folded.

Therefore, you need to press the silvery retainer plate away from the hook (push up) to allow the loop to be slid from the hook. The belt was tight with the seat back in the upright position, so it was necessary to fold the seat back forward to create slack in the belt. Now push the belt loop towards the trunk and slide it off of the end of the hook (only possible with the retainer plate pushed up out of the way).

Now with total release of tension on the system via the bottom end of the seat belt being untethered and with the seat back returned to the upright position, normal extension and retraction of the belt will be reestablished. Next, simply extend the seat belt and slide the loop back into place over the floor hook. It snaps past the silvery retainer plate without all the effort required to hold the plate up during removal of the loop during disassembly.

Check again, the seat belt should be extending and retracting properly. Now just put the seat cushion back into regular position and you will be able to safely buckle up three people across the back seat.

It took about as long to do this repair as it has taken to post this answer to the problem. Note, the seat belt safety mechanism only allows normal extension and retraction of the belt when the seat back is upright.