89 Dakota 2WD 3.9 V6. Pedal goes to the floor with engine on or off. Won't pump up to a hard pedal. No leaks, MC full. With engine off, pumping pedal, I hearing a swooshing air sound. Brake light does come on and off when running. I can stop, but its not safe. No intake leaks at power booster hose or check valve. Bad valve?? I should add that sometimes the MC needs fluid and the rubber gasket on the cap has popped its nipple. But again, no visible leaks??