51 22 004 Adjusting rear left or right door detent (lock wedges)
WARNING: This page does not describe the selected car, but rather 19 other vehicles, including the 2010 BMW M5, 2009 BMW M5, 2008 BMW M5, 2007 BMW M5, and 2007 BMW 550i. However, it is still accessible from the selected car via links, so may be relevant.
Operation is described in:
51 21 004 Adjusting front left or right door detent (lock wedge)