The airline transport pilot was on a Title 14, CFR Part 91, personal cross-country flight with three passengers when the accident occurred. The pilot said during the landing roll he noticed that the right main landing gear brake did not work. He said he tried to land straight ahead, but the airplane drifted to the right side of the runway, and then ground-looped to the left. He reported that the right wing, aileron, horizontal stabilizer, and elevator were damaged during the ground-loop. He said there were no known mechanical problems with the airplane prior to the accident. The pilot said an examination of the right brake revealed that the set-screw holding the right brake cylinder cap in place had not been properly installed, and allowed the cap to come off the cylinder, and jam the right rudder/brake pedal.