On September 10, 1999, approximately 1345 Pacific daylight time, a Cessna 170B, N3476D, sustained substantial damage when it struck VASI lights during landing roll at Auburn municipal airport, Auburn, Washington. The commercial pilot, the sole occupant and registered owner of the airplane, was uninjured. The flight, conducted in visual meteorological conditions under 14 CFR 91, originated at Puyallup, Washington, about 20 minutes earlier. There was no report of the ELT actuating, and no flight plan was filed for the flight. The pilot stated that he had made a three-point touchdown on runway 34. Shortly after touchdown, he felt very heavy shaking or vibration from the tailwheel and the airplane "veered violently to the left." He attempted to correct with right rudder and right brake, but was unable to bring the airplane back onto the runway. The airplane was observed to depart the left side of the runway at a low speed and impact VASI lights, damaging the right side aft fuselage and the elevator. Witnesses noted that they could hear the vibration from hangars adjacent to the east taxiway, and could see the tailwheel jerking to the right and left, after what was described as a very smooth touchdown. The pilot stated that his approach speed was right at 70 miles per hour, and his touchdown speed was somewhere between 45 and 55 mph. FAA inspectors inspected the damaged airplane and noted that the right brake cylinder was leaking. Additionally, the tailwheel casting was loose at the attachment point with the tailwheel leaf spring.