A common fault for these projectors is the clutch gear failing. The two circular keys on the centre of the gear are eventually ground out by the metal axle they sit on. If this happens the mirror door will flap about and not open/close correctly.
I've knocked this replacement part up in TinkerCAD - it's not exactly the same as the OEM gear, but it's close enough that it works.
I'm printing these in ABS and have had good success with them, but I think PLA might be a better choice as it needs to be very strong to not have the key in the middle ground out by the metal axle it sits on.