You'll have to check the manual for the exact procedure to test the master cylinder. One thing you might try..... I replaced the bars on a non-RC51. I wanted to reposition the brake line. One expert on that bike, advised that the front brakes on that bike were a bitch to bleed. Another user replied that you could tie back the brake lever (in the actuated position) over night, and any air in the line would travel upward toward the reservoir. I haven't tried it myself, but it's easy enough to try.