common on golfs too. you find if you out the seat down you eventualy wont get it up again as the belt tightens when its down and digs in the seat once put back up.
if you can, take the tension off the belt, by unclipping it from the underneath the seat, you can feel the rind that clips on the floorpan hook, with some force you can unhinge it and then the belt is loose . you will then find it will retract and extend at will.
what you now need to do is pull some slack out so the belt once reconnected is a little loose over the seat pad, then mark the belt position whenre it goes through the guide on the seat back/side, ie where your shoulder is. Then get some rivets or even jeans buttons (from sewing shop) and put a rivet button through infornt of the shoulder guide to stop the belt retracting too far and going under tension.
Thsi certainly hlped my golf and its good now 3 years on, but I am afraid the mechanisms are a bit crap in the back and eventually it will go bad and need replacing.
