Hi, hope someone can help. We have fixed new curtain tracks to our bay window (1930's house). They are the new sort with plastic locking fixings. They are PVC and are for medium weight curtains. Our curtains are medium weight. The problem is that one of the tracks keeps falling down when the curtain is being pulled open. One of the little plastic "keys" that goes into the locking fixing on the wall has now sheared off. Can anyone suggest what we can do to stop the curtain rail falling down?