WARNING: This page is about a different car, the 2010 BMW 135i, 2009 BMW 135i, and 2008 BMW 135i. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Guide Pins (2 x) (23 1 450)
Courtesy of BMW OF NORTH AMERICA, INC.
NOTE:
For fitting bearing bush in locking device of guide sleeve