Brake light stays on pedal goes to floor front chamber of Master cylinder keeps going dry

Sometimes brake fluid leaking from a rear wheel cylinder takes a while to show up, but to be leaking fast enough to have the pedal go to the floor, it should be pretty easy to find it. If nothing else can be found, loosen the bolts on the master cylinder and pull it forward to see if fluid is leaking out the back and into the power booster.