THE AIRPLANE RAN OFF THE END OF THE RUNWAY AND DOWN AN EMBANKMENT AFTER THE LEFT BRAKE FAILED DURING LANDING. THE PILOT SAID HE HAD BRAKES ON THE RIGHT, BUT NOT THE LEFT. THE FAA EXAMINED THE AIRCRAFT AND FOUND THE LEFT BRAKE WORN TO THE POINT THAT THE PISTON EXTENDED BEYOND ITS NORMAL RANGE AND ALLOWED THE SEAL TO LEAK AND THE BRAKE TO FAIL. THEY ALSO SAID THE RIGHT BRAKE HAD FAILED IN A SIMILAR MANNER 4 HOURS PRIOR AND THE OWNER HAD INSTRUCTED THE REPAIR FACILITY TO ONLY REPLACE THE LININGS ON THE RIGHT SIDE.