i seen a few threads regarding this issue but i wanted to explain exactly what happened with mine. I was riding in a gravel pit hitting jumps, etc. and my brakes were fine, and then all of a sudden i went for the back brake and the pedal went through the full stroke and didnt give me any braking power. it will not build any pressure at all when pumping it. When it happened there seamed to be an oily film on the master cylinder but when i try and pump the brakes now, there are no apparent leaks and no film on the master cylinder.
I may have gotten a bit of air in the line a couple nights ago when i opened the bleed screw with the brake pedal up, however i couldnt get any pressure before that anyways.
So would my best plan of attack be to bleed the brakes properly, or would you assume that there is a failure in the master cylinder?