What was found
LOW BRAKE PRESSURE WARNING ILLUMINATED DURING TAXI, RETURNED TO GATE AND SHUT DOWN WITH NO DIFFICULTIES. PILOT NOTICED FLUID ON THE GROUND UNDER NOSE, IN THE VICINITY OF THE BRAKE PRESSURE PUMP. MAINTENANCE INSPECTED AND FOUND AN O RING BLOWN OUT AT BRAKE PUMP FILTER HOUSING, A NEW O-RING AND FILTER WERE INSTALLED, BRAKES BLED AND OPERATIONALLY CHECKED OK.