I have the dual piston cast iron big brake kit on my Monte with the 13 inch rotors. Today i went to my local O'reilly's and bought two replacement rotors, same size 12.71" and same bolt pattern, BUT the rotor vanes are directional, not straight!? Found out that they gave me either two left rotors or two right rotors, and now i have one rotor vanes going against the forward rotation and the other the opposite way. Anyway i tried explaining this to them, the manager seems to understand but the rotors only come in one part number and no left and right, just a pair of rotors, seems like there's a glitch in their system or something. Anyways im going back tomorrow to maybe get a right side rotor if not i'm returning these sweet babies until i figure something out. damn headache with this