The pilot of the experimental, amateur-built tailwheel airplane was also the owner and maintained it as well. He stated that during landing, the right main wheel locked up and the airplane veered right. The pilot immediately released right brake pressure and increased left brake pressure, but the airplane continued to veer right off the right side of the runway and came to rest inverted in a grass area. The pilot subsequently examined the right brake under the supervision of a Federal Aviation Administration inspector. The brake piston tested satisfactorily, and the pilot could not duplicate a brake locking event. He noted that one of the two caliper pins and one of the two pressure plate holes were worn beyond specification. The pilot added that the wear could cause the pressure plate to cock, or foreign object debris to enter, and cause unintended braking.