What was found
FL320, THE RT BRAKE PRESS GAUGE INCREASED O TO 2000 PSI. AFTER 12 MIN IT DECREASED TO 1500 PSI. AFT 30 MIN IT DECREASED TO 400 PSI. BRAKE A/S SELECTOR WAS IN THE NORMAL ON POS. ALL WHEEL BRAKES SHOWED REL ON ECAM. PARKING BRAKE WAS VERIFIED OFF. LATER IN THE FLIGHT FROM OAK, THE PROBLEM REPEATED. DURING DESCENT RT BRAKE PRESSURE DECREASED TO ZERO. NORMAL LNDG. PERF OPS TEST OF ALT BRAKING SYS PER MM 32-43-00. OPS CK OK. PERF OPS TEST OF PARKING BRAKE SYS PER MM 32-45-00. OPS CK OK. REMOVED AND REPLACED BRAKE YELLOW PRESS TRIPLE IND MM 32-44-19-4 PRECAUTIONARY. REMOVED AND REPLACED YEL BRAKE SYS PRESS TRANSMITTER 72GG.