Two things commonly restrict brake fluid from returning freely to the master cylinder. A rubber flex hose can become constricted or a seal in the master cylinder has swelled and has grown past the return port causing it to be blocked. It is unlikely two front hoses developed this problem at the same time. If just the left brake is dragging and getting hot, suspect the hose. If both front brakes are affected, suspect the brake fluid is contaminated with a petroleum product such as engine oil or power steering fluid.