2.0 Grinding outer shell and structure
WARNING: This page is about a different car, the 2011 BMW 750xi, 2011 BMW 750Lxi, 2010 BMW 750xi, and 2010 BMW 750Lxi. However, it is still accessible from the selected car via links, so may be relevant.
Always replace abrasives which have already been used to treat aluminum (risk of corrosion).
Do not grind the material thin.