the rear brake on my 09 pro works fine when you press it , but when you apply continual pressure it looses the peddle, ive replaced the seals in the caliper and there dosent seem to be fluid leaking from anywhere, i eventualy managed to bleed it and get a good peddle but after a few pumps the problem returns and i get a little air at the bleed nipple as if air is been drawn into the system, ive bled the system so many times that the air must be out as it couldent of worked with the amount of air thats came out. any ideas?