As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT EXPERIENCED LOSS OF LT BRAKES DURING TAXI TO RUNWAY. PILOT WAS ABLE TO STOP WITH OTHER BRAKE AND ELECTED TO HAVE AIRCRAFT TOWED TO PARKING. NO PRESSURE WAS EXPERIENCED WITH OPERATION OF BRAKE. REMOVED MASTER CYLINDER AND FOUND AN O-RING WAS WORN FLAT AND WAS VERY STIFF. REPLACED THE O-RING AND BACK-UP SEAL AND INSTALLED MASTER CYLINDER BACK IN AIRCRAFT. BRAKE PRESSURE WAS SATISFACTORY. TAXIED AIRCRAFT, BRAKES PERFORMED SATISFACTORY. AIRCRAFT RETURNED TO SERVICE.