51 21 004 Adjusting Front Left Or Right Door Detent (Lock Wedge)
WARNING: This page is about a different car, the 2008 BMW Alpina and 2007 BMW Alpina. However, it is still accessible from the selected car via links, so may be relevant.
Operation is described in:
Adjusting left or right front door . See 41 51 004 ADJUSTING LEFT OR RIGHT FRONT DOOR .