Sounds like you need to purchase a new seatbelt receiver. They're about $40 a piece and IMO, not worth trying to fix since it's a safety-related item that you want to work properly.
http://www.ebay.com/itm/191090213008?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT