The original brakes on my '54 Mercury worked just fine but I noticed some seepage of brake fluid on the inner side of the right rear backing plate so it was obvious that the wheel cylinder was leaking.  I bought a new Dorman wheel cylinder at NAPA and installed it.  I inspected the shoes which were almost new.  I bled that line and readjusted the brake so that the shoes were very slightly dragging on the drum.  I drove the car about 15 miles one way to a local show.  As I got close to the location, I could feel that the brakes were dragging.  By the time I got to the show the right rear hubcap and wheel were very hot to the touch and that side was smoking (very embarrassing).  I was able to drive the car home with the brakes only slightly dragging.  The brake dragging problem continued to persist on that side.  I removed the drum to inspect the situation and the dragging had succeeded in wearing the shoe material down almost to the shoe metal.  All I can think is that the new wheel cylinder must have been defective and sticking in the outward position rather than retracting with the spring tension when the brake pedal is released.  Has anyone ever had a similar problem?  Could there be some other cause rather than the wheel cylinder?   All of the brake hardware was replaced when I restored the car.