My 108 car, a 1972 280SE 4.5, has a problem with all four brakes sticking from time to time. This occurs after the car has been driven a ways and goes away after the car cools off. I suppose it could be the flexible portions of the brake lines but it would seem unlikely since all 4 corners stick simultaneously. My local indy suspects it's a booster problem, and I also suppose the master cylinder could be at fault. How does one test these parts of the system? Any thoughts or advice would be welcomed.

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1972 280SE 4.5