On September 8, 1999, about 1630 Alaska daylight time, a tailwheel equipped Stinson 108-2 airplane, N97978, received substantial damage while landing on runway 19 at the Birchwood Airport, Chugiak, Alaska. The first pilot, a certificated flight instructor, seated in the right seat, and the second pilot, a certificated private pilot, seated in the left seat, were not injured. The airplane was being operated as a visual flight rules (VFR) local area instructional flight under Title 14, CFR Part 91, when the accident occurred. Visual meteorological conditions prevailed, and no flight plan was filed. During a telephone conversation with the NTSB investigator-in-charge on September 10, the first pilot reported that he was providing tailwheel transition flight instruction to the second pilot. He said that eight successful stop and go landings had been accomplished prior to the accident landing. He stated that while landing on runway 19 and during the landing roll, the second pilot applied the brakes. The airplane subsequently ground looped to the right, and the left wing struck the ground, resulting in substantial damage to the left wing. The first pilot reported that brake pedals were only installed at the left side pilot position. After the accident, the second pilot related to the first pilot that during brake application, the left brake pedal "felt mushy" and was less effective than the right brake. A Federal Aviation Administration (FAA) airworthiness inspector, Anchorage Flight Standards District Office, examined the airplane at the accident airport on September 10. He reported signs of brake fluid leaking from the left brake assembly. He added that disassembly of the left brake assembly revealed "severely weathered and worn seals."