There is a plastic "circlip" on the end of the mirror shaft that stops the full extraction of the mirror. This is in addition to the plastic conical "washer" you can see at the end of the stem - it is easier if you slide this up the shaft before trying to pull the standard mirror out. I removed the stem screws completely. More force required - but not so much that you damage the base or door. Once you have done the first one you will be happier.
Good luck.
