To remove the ext. mirror, one needs to be able to access the points, where it is fixed. And those points are hidden under that "triangle" inside, which on other cars is just that, a "triangle", but on the X-Type it is one part with the complete inner plastic frame. I pulled out the inner door trim just a little bit after removing that screw (hidden under a plastic cap behind the grip, where you grab the door to close it. Then I pulled off the "frame" starting at the left lower corner.