From GTM Workshop

Problem

A common problem with the Libra is that the threaded balls that are used to secure the removable roof section can work loose, and eventually drop off. They will usually end up under a seat somewhere.

Solutions

For those that find this annoying there are some possible remedies:

1. Use a nyloc nut instead, it looks awful but works
2. Put some loctite on the bolt
3. Put a drop of silicone sealant in the bottom of the hole in the ball, this will give the bolt something to go against and stop the vibrations
4. Place some sort of rubber washer between the ball and the roof to the same effect as 3
5. An alternative fixing can be used, see Libra Quick Release Roof Catches