The pilot of the tailwheel-equipped airplane reported that he made a normal landing approach to the runway with a direct crosswind of 15 knots and gusts reaching 23 knots. The pilot reported that he was initially able to maintain directional control with normal flight control inputs after the airplane touched down on the main landing gear; however, when the tailwheel touched down the tail began to weathervane and the airplane veered to the right. The pilot was unable to regain directional control with an application of full left rudder and left brake before the airplane departed the right side of the runway and struck a precision approach path indicator lights (PAPI) system. The left wing, left horizontal stabilizer, and left elevator were substantially damaged during the collision with the PAPI system. A postaccident examination and functional test of the steerable tailwheel revealed that the spring-actuated key slide would stick in the retracted position within the tailwheel fork, which allowed the tailwheel to caster instead being steerable within the normal limits intended for takeoff and landing. Additional examination revealed that the slot in the tailwheel fork that held the spring-actuated key slide was slightly deformed, and that the key had several raised edges that caused the key to bind when fully retracted in the slot. It is likely that the tailwheel was able to caster during landing, which resulted in the pilot's inability to maintain directional control after the tailwheel had touched down during landing roll.