Try P21S Metal Finish Restorer. Works like magic...I use it on my tips once a month or so to get the black stains off.

http://www.detailersdomain.com/p21sf...talpolish.aspx

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2009 E90 M3 M-DCT | Alpine White/Black/Carbon

SOLD: 2008 X5 3.0si | Black Sapphire/Black Perforated/Burl Walnut | Premium | Sport | Cold Weather | Premium Sound | Active Ventilated Seats | Auto Tailgate | Comfort Access | Running Boards | Heated Rear Seats | PDC | OEM 20" Style 214s | Titanium Kidney Grilles | Tint 20% Rear/35% Front | GP Thunder 7500K Halos | Xenesis Fogs