I dont think its a bleed problem, they bleed themselves. They also have an accumultor (pressurized cylinder) that stores pressure if the pump pressue is lost or the engine stalls and pump quits turning. It supplies assist for the brakes if such a condition occurs. The accumulator is the big round cylinder shaped thing on the hydra boost.
sounds to me like you need to install a new hydra boost.I would also check the pressure valve in the pump( inside the pump, behind the pressure line fitting) if it has debris in there it too can cause issues.
Fact is stranger than Fiction