I have a '06 Harley Dyna and the rear brake rotors warped after 3,000 km. I live in Tokyo and am new to motorcycles. The Japan HD dealer said I must be braking too hard <-- this is not a superbike but a cruiser and I commute 2 km to/from work. Anyway, they said it is not covered under warranty and I had to pay 50,000 yen ($450) to replace. Any advice...was I taken? Is it normal for rotors to warp or is it poor rotor quality?