This is a classic failure of the master cylinder, leaking from one 1/2 of the system to the other. Replace or rebuild the master cylinder.
I'll add that this failure mode usually includes brake fluid leaking into the booster; replace that also for safety and for your cousin and mine, Justin Case.This is a classic failure of the master cylinder, leaking from one 1/2 of the system to the other. Replace or rebuild the master cylinder.