LRP Bonded Rotor Turned BLACK???

[NSDie]

I have a LRP 5.5 bonded motor which was running fine for about 6 months until today. It just stopped running in the middle of a race. For the first time, I opened the can and took the rotor out. It was black!! Is that the normal color of a bonded rotor? Also I connected my speedo to another motor and it was working.

I need to know what could be other causes of motor failure. It is worth it for me to buy another rotor to test it out or just forget about it and buy a new motor?