the seatbelt fasterne on the newer models (95-) have an incedury (sp) in the belt lock, that fires inwards onn impact.
there is a wire that is coupled up to th SRS system, and this works loose or snaps after repeated wear on the seatbelt ( i never waer mine anyway, bad i know)
a clever mechanic will repair and secure this wire. BMW may just replace it.
Fault diagnose via tester will say where the fault is
