another thing is - if someone has broken the arm - it'll obviously not work
My new M3 driver side has a bit broken inside the arm.............. which means the little lever on the end stays floppy - meaning it doesn't stay out at a right angle to the arm itself........... its floppy and flops back to about 45 degrees from the arm and loses the belt
The lever on the end of the arm should remain stiff at 90 degrees - and only once it retracts should it flop back - to allow it to sit back into the door panel.
Pointed it out to the garage and they're gonna replace the arm
Max