I believe the rusty part is the brake pad retaining clip. Part 34116799386 on standard braking systems:
http://www.realoem.com/bmw/enUS/show...diagId=34_2455
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F10 530d M Sport, September 2012 Individual Amazonite Silver, Oyster Dakota Leather, Auto, Nav Pro, Bluetooth + USB Devices, Expanded BMW Online, Comfort Seats, Sunroof, Sun Protection Glass Individual Satin Walnut Honey Brown Trim Interior Inside/Outside Mirror with folding and autodip, M Rear Spoiler