Anyone know about hinges for double-glazed windows? I have a couple which won't pull the window tight closed at the top, there's about a 6mm gap left. From what I can see there's a tongue on the opening part of the hinge which should run up a wedge-shaped part on the fixed part to close the hinge tightly but it doesn't seem to be making contact. I can't see any adjustments on the hinge, and nothing seems to be loose or broken. Any ideas?