The pilot stated that he was conducting a personal flight with the owner of the airplane. The owner did not have any flight time in make and model. The airplane had a pre-buy inspection conducted two days before the accident and no anomalies were noted. The pilot conducted a preflight inspection before the flight and no anomalies were noted. The pilot and the owner departed on runway 36 and remained in a left closed traffic pattern. The pilot made a three-point landing in the first 1,000 feet of the runway, and was on the landing roll out, when the tailwheel started to shimmy. He applied forward pressure on the control stick and raised the tailwheel off the runway. The shimmy ceased and the pilot applied aft pressure on the control stick and lowered the tail wheel onto the runway. The airplane immediately veered to the right. The pilot applied left brake and rudder, but the airplane continued to the right off the right side of the runway and collided with a ditch. The right main landing gear separated and the right wing received structural damage. Examination of the airplane revealed the right spring on the tailwheel control had separated from the rudder and the tailwheel attachment. The tailwheel spring was located about 20 feet off the right side of the runway and there was no visible damage to the tailwheel spring or the upper and lower attachments points. The previous owner stated that he informed the new owner of the tendency for the tailwheel to shimmy during the three-point landings.