The rust on the RBs is from metal particles in the brake dust that settle on the RBs and rust. I've had good luck with using a high quality wheel cleaner to remove the rust spots on them...

__________________

2008 4.8i X5 (2/25/08) 105k:
Titanium Silver/Black; All -HUD; Aero Kit; 22" VS-130 w/Pirellis;
///M Shifter & Fr Brakes; Gauge Rings; Console Pads; Custom Wheel & Mats; Roof Rails
Carbon Fiber: Int Trim, Nav Surround, Grill, Cluster Trim, Shifter & Eyelids
1.2" H&R; LUX AEs; LCI Tails; Rear Fogs; NBT EVO; ESS Tune; Meisterchaft GTC Exhaust