There are 2 MDF ears or tabs that stick down from the top when opened for service. The locking rods go into these when closed. One or both of these may be loose or the hole for lock to slide into is over sized on them. If they're hogged out and sloppy, you can order replacements on line from different sources. Let me know what you find out. I can help you with lining things up and marking new hole if you have to replace. Pics would also be helpful. tydy