What was found
(CAN) PILOT REPORTED GETTING A VIBRATION WHEN APPLIED BRAKE PRESSURE WHILE SLOWING DOWN AFTER LANDING AND EVEN WHILE TAXING. ENGINEERS INSPECTED THE BRAKES AND FOUND THE NR 4 POSITION BRAKE WORN TO LIMITS. BRAKE WAS REPLACED AND SENT TO THE BRAKE SHOP. THE UNIT WAS OVERHAULED AND PRESSURE TESTED, THAT IS WHEN DISCOVERED THAT A PISTON HOUSING WAS LEAKING. THE UNIT WAS DISASSEMBLED AND SENT FOR NDT INSPECTION WHERE THEY FOUND A CRACK IN THE SIDEWALL OF A PISTON HOUSING IT WAS DETERMINED TO BE BEYOND LIMITS SO THE ASSEMBLY WAS SCRAPPED.