On September 25, 2000, at approximately 1015 mountain daylight time, a North American T-28D, N28YF, was substantially damaged when the nose gear collapsed during landing roll at Russ McDonald Airfield, Heber City, Utah. The airline transport pilot, the sole occupant aboard the airplane, was not injured. The pilot was operating the airplane under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the local flight that originated approximately 20 minutes prior to the accident. No flight plan had been filed. The pilot said that during the landing roll the nose wheel began to shimmy. As the airplane slowed down, the shimmying became worse. He said that as the airplane approached 40 knots, the nose landing gear collapsed, and the propeller began striking the runway. The airplane sustained structural damage to the firewall and its bulkhead. Postaccident examination by Engineering Systems, Inc., Aurora, Illinois, determined that the nose wheel shimmy damper had malfuctioned. They determined that there was grit behind both cylinder end caps, and there was evidence of a slow hydraulic leak from the damper.