I took it off the door and discovered that the internal cast aluminium structure that secures the internals had sheared in half allowing the two parts of the mirror to separate as you can see in the picture.
![Image](http://i271.photobucket.com/albums/jj138/7builder/BMW%20X5/imagejpg2.jpg)
The reason I didn't notice a problem when I bought the car is because despite the obvious internal failure the mirror still adjusted and dipped when reverse was selected. I didn't check if the mirrors folded (which this one obviously wont) because I didn't know they could. :-[
Is it possible to purchase the internals to repair the mirror or do you have to buy a complete replacement wing mirror? I did a quick search on ebay and required the administration of smelling salts when I found out how much that second hand units are going for.