On April 23, 1995, about 1430 eastern daylight time, a Stinson 108-2, N978D, piloted and owned by Dan D. Kibler, on a personal flight, was substantially damaged during landing at Clarion County Airport, Clarion, Pennsylvania. The pilot was not injured. Visual Meteorological conditions prevailed. The flight was being conducted under CFR 14 Part 91. In the NTSB form 6120.1/2, the pilot stated, Was making normal landing at Clarion County Airport on runway 6. Airplane was on the runway in a final roll out, when a gust of strong wind caught the left side of tail and turned aircraft to the left. Right brake failed and was unable to make necessary correction to keep airplane on runway....[The] airplane veered to [the] left [and] went down over high embankment and nosed over. An inspection of the airplane's brake system was performed by Shippenville Aviation, Shippenville, Pennsylvania under the supervision of a Federal Aviation Administration Inspector. The inspection revealed that both brake pedals were slightly spongy. However, when the right pedal was released slightly, and then reapplied, it would bottom out and go to the floor. This test was performed several times, with the same results each time.