I've sheared 3 keys on this bike. The 1st is a mystery. 2nd and 3rd it turns out that I read the torque spec wrong. So, that's most likely the cause. My buddy told me to put valve grinding compound on the shaft and slide the rotor on with no key, and snug the nut and spin, spin, spin it. Remove it and putmore on and repeat. So, I'm doing that and I noticed this small nick. Is that a problem?