Brake fuild leak?

[Staffsargent]

Today I notice that the brake pedal was a little low. Checked the master and is was almost empty. Pulled all the drums and checked the wheel cyls (all dry). Checked the brake lines and no leaks. Put every thing back together and adjusted the brakes. My question is, where did all the brake fuild go? Does anybody have or had the problem?

 

[Recovry4x4]

Might have been pushed out the vent from the airpack. I've also found a master cylinder leak down at the boot and didn't notice it for it was on sand.