2.1 Steel surface

WARNING: This page is about a different car, the 2013 BMW 550i GT, 2012 BMW 550i GT, 2011 BMW 550i GT, and 2010 BMW 550i GT. However, it is still accessible from the selected car via links, so may be relevant.

Grind bonding surface with a metallic bright finish for better adhesion.
Clean bonding surfaces with cleaning agent R1.
Allow cleaned surfaces to dry for approx. 5 minutes.
Bonding surfaces must be completely dry.