The private pilot reported that he was taxiing for takeoff on a personal, cross-country flight under Title 14, CFR part 91, when the left brake locked. According to a witness, the pilot stated that he had serviced the brakes prior to taxiing. A mechanic repairing the airplane said he found that the left brake was over-serviced with fluid, and that the right brake linkage was improperly adjusted, leaving the left brake tight, and the right brake loose. The airplane sustained damage to its wings, wing spars, and horizontal stabilizer.