I would use a small amount of Silicone thinly wiped around the stud and inserted back into the bobbin. Never use a permanent glue as you may want to have the pickups repaired and the glues could alter the shape of the bobbin. A thin layer of wax could coat the stud and insert it back into the bobbin. This can happen when molding the bobbin and certain plastics have different shrink tolerances. Also the plating on the stud could be too thin, leaving the part under spec. Consult the manufacturer too so he can solve the problem.