Just had a member ask me about mirror glass removal. Forgot I had taken pics when I swapped mine for folding and had meant to put them here for reference.
If you tilt the mirror glass fully downward, you will see the tab on the locking ring as circled below;

You need to use a screwdriver in the slot to move it anti clockwise to unlock and vice versa to lock. The pics below show how the ring works to uncover the motor lug mounting holes;


Mike
If you tilt the mirror glass fully downward, you will see the tab on the locking ring as circled below;

You need to use a screwdriver in the slot to move it anti clockwise to unlock and vice versa to lock. The pics below show how the ring works to uncover the motor lug mounting holes;


Mike