Not sure if the 911 sun visor mount is similar to the Boxster's but the threaded female portion of the visor mount on the Boxster is a common failure. One solution is to replace the original threads with a nutsert.
randrcenternuts - mikefocke2
I was able to do a temp fix on mine using black silicone sealant, and it has lasted several years. At some point I'll probably go the nutsert rout if needed.
Aron