As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TAXI, THE LEFT BRAKE MASTER CYLINDER PISTON SNAPPED OFF AT THE RUDDER PEDAL CONNECTION JUST BELOW THE JAMB NUT. THE AIRCRAFT RETURNED TO IT`S PARKING SPOT. THE PILOT INFORMED MAINTENANCE THAT THE BRAKE WAS "LOOSE". MAINTENANCE REPLACED THE PISTON AND THE AIRCRAFT WAS RETURNED TO SERVICE.