brake pedal gets very hard and fluid is escaping!

[Tom Tom Turbo]

So, I was coming to a normal stop, when I hit the brakes and the pedal goes in about an inch, gets very firm, and the car doesn't stop. After gently driving it through a ditch, throwing it in neutral and getting it stopped, I realize that brake fluid is oozing out the top of the powermaster. I cannot see where it is coming from exactly, but the resivoir is still full of fluid. What is going on here? I have a new GM powermaster in the bullpen, is it time to start warming 'er up?