I have a 2003 Yamaha raptor 660, and i rebuilt the master cylinder and rear caliper, but after each hard ride, i need to bleed the rear brakesbecause they loose pressure, I have read about the recall on the raptor660. So i called Yamaha and how I bought the bike used i didnt know if the previous owner took it to the dealer, which they did and had the recall so called fixed. I still think it is the vibration in the reservoir.