On January 10, 1998, about 1240 eastern standard time, a Cessna 170, N48021, registered to a private owner, operating as a 14 CFR Part 91 personal flight, ground looped on landing at Orlando Executive Airport, Orlando, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The airplane sustained substantial damage. The commercial pilot and two passengers were not injured. The flight originated from Leesburg, Florida, about 20 minutes before the accident. The pilot stated he was making a wheel landing to runway 25. The airplane started to veer to the right on landing rollout. He did not attempt a go-around. He lost directional control. The airplane continued to the right, collapsed the left main landing gear, and the left wing collided with the ground sustaining structural damage. The pilot contacted the NTSB on March 23, 1998. He stated his airplane had been repaired and returned to service. During the repair of the airplane by Aeromasters, it was determined that the left brake master cylinder was inoperative due to a bad o-ring.