The factory-optional compass/autodimming mirrors on the 2008-2014 Impreza/WRX/STI cars have kind of a funny attachment system, and one part has screw holes that are not threaded — the screws themselves cut the threads as they are installed. Inevitably these threads seem to loosen up. Sometimes the mirror is loose straight from the showroom. (You could bring the car back to the dealer under warranty, but who has the time for that?)
The solution to the wobbly mirror is this kit, which includes some extra parts you don’t need, but also includes a brand new copy of the one part you do need. Installs easily with a Phillips screwdriver and a T20 Torx driver. Be careful NOT to over-tighten the Phillips screws!
Fits all 2008-2014 Impreza/WRX/STI with compass/autodim mirror. Also fits 2013+ FR-S and BRZ with the same option.