RF brake locked up. Why?

Returning from the transmission shop with my newly restored (all stock) 1965 Barracuda I decided to drive down to a gas station and get gas. About a mile away the brakes started to fade out. Near the gas station smoke started coming out of the right front fender. At the gas station I saw that brake fluid had sprayed around the right inner fender well area. When I then tried to move the car I found it was locked up and the rear tires squealed. I called a tow truck and while waiting for it I found the RF Wheel brake had then freed up.
I have not yet started to take it apart. I had DOT 7 fluid in it.
What do you think happened and what do you think will have to be done and replaced?