On February 10, 1999, about 1115 Eastern Standard Time, N87464, a Cessna 310R, was substantially damaged while taxiing at the Sullivan County International Airport (MSV), Monticello, New York. The certificated airline transport pilot, and commercial rated second pilot, were not injured. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the training flight, which originated from Teterboro Airport, Teterboro, New Jersey, conducted under 14 CFR Part 91. The pilot stated that the airplane landed on Runway 33, a 6,300-foot long asphalt runway, with the second pilot, who was in the left seat, at the controls. After the landing, a left-hand turn was made onto taxiway "Charlie." A second turn to the left was then made onto taxiway "Alfa," a 75-foot wide, down sloping, asphalt taxiway. The pilot added that the brakes appeared to operate normally during all of the turns. The airplane continued to taxi, at a speed of "about a fast walk," to the active runway for departure. Due to the strong winds, the power was at idle and light braking was used. As the second pilot began a left 90-degree turn to the runway hold short line, he commented that there were no brakes. The pilot then took the controls and attempted to depress his brakes with no result. The airplane continued to roll, veering to the right into a grass ditch, about 20 feet from the taxiway. The airplane came to rest straddling the ditch while being supported by the nose and tail. The pilots reported testing the brakes prior to their departure from Teterboro Airport, and found no irregularities. There was a maintenance discrepancy written prior to the accident flight regarding the brakes installed on the airplane. During the corrective action to fix the discrepancy, a faulty Lock-O-Seal was found, and replaced. Examination of the airplane after the accident by a Federal Aviation Administration Inspector revealed sufficient brake pedal travel and pressure on the left side brake pedals. According to the 1975 Cessna Model 310 Owner's Manual, "A steerable nosewheel, interconnected with the rudder system, provides positive control up to 18 degrees left or right, and free turning from 180 degrees to 55 degrees for sharp tuns during taxiing. Normal steering may be aided through the use of differential power and differential braking on the main wheels. These aids are listed in the preferred order of use." The winds reported by MSV, at 1045, were from 300 degrees at 18 knots, gusting to 26 knots.