The part you need to replace is called the "cap", I just did mine, $37 for black $72 for chrome, got the part #s from Max BMW parts fiche on line. ordered from my local dealer. The easy way to separate the mirror from the back plate is to push the back plate away from the mirror just enough to drip some rubbing alchol behind the mirror , this will debond the adhesive, you will have to keep pushing the back plate away from the mirror to separate it. It takes a few minutes , you will have add more alcohol as the mirror comes apart. Once the mirror is off the are 4 screws to separate the " Cap" from the painted body part.