My '54 Merc brakes are building pressure even sitting in the garage and the car not running. If I leave it running the brakes will almost lock up and only release after the car is shut off for quite a while. Today I turned on the furnace in my shop and within two hours the brake lights were on (car not running). It has a Midland power booster ('55-57 T-Bird type). Any suggestions?? Thanks : Bruce