During the landing as the tailwheel touched down on the runway, the tailwheel began to shimmy, and the airplane drifted left of the centerline. The left seat pilot attempted to maintain control, and the right seat pilot twice made minor inputs to maintain the centerline and “lifted the tailwheel” to alleviate the shimmy. When the tailwheel touched down a third time and the airplane’s full weight was placed on the tailwheel, the airplane veered sharply to the left. Full application of the right rudder did not correct the left turn, and the airplane ground looped. Substantial damage was sustained to the airplane’s left wing. A postaccident examination of the airplane found that the steering arm of the tailwheel assembly had been contacting tail structure in a location that was only visible when the tailwheel suspension and steering assembly had been removed and not during the routine annual inspection. It is likely that the airplane’s weight load on the tailwheel compressed the area enough due to excessive wear to restrict steering and rudder control during the landing. The airplane had accumulated 2 hours of flight since the most recent annual inspection.