Naaa, my calipers have surface rust on the outside too, but they operate just fine. Replace your calipers if you notice your brakes start to stick on one or more wheels or if they start to leak. I agree with 325is, replace both the rotors and pads on all 4 wheels. OEM parts, if purchased by you from an online wholesaler, should run you no more than $300 (don't forget the pad sensor wires and silencer goup!!!). Either do the work yourself or take it to a reputable mechanic in the area... take it to the dealer if it's covered by the warranty.