Rear master cylinder problems...

[MACROMOLECULE]

2012 GasGas EC300R
Nissin Rear Master Cylinder "11" BE660002509

So I need some help here. Right now my rear brakes are completely nonfunctional. I was bleeding the lines to remove air bubbles by depressing the foot lever a few times and cracking open the bleed screw, quickly shutting it and repeating the process. Things were going well when all of a sudden I lost all resistance in the foot lever and now when I depress the lever very little brake fluid is being pushed through the lines even with a wide open bleed screw. There's no external leaking that I can see. Do you think I broke the master cylinder? Or does this sound like it can be repaired with a rebuild kit. If it is a simple rebuild which kits will work for this master cylinder? I can't seem to find much information on a nissin-specific kit. Any advice?