What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS DURING DESCENT ON AUTO-PILOT AIRCRAFT ABRUPTLY PITCHED DOWN - AUTO PILOT DISENGAGED AND ECAM INDICATED B+Y SYSTEM FAILURE - MOMENTARILY - RECOVERED AIRCRAFT - BLUE SYSTEM INDICATIONS RESOLVED ON THERE OWN- HAND FLEW APPROACH. ON WALK AROUND AFTER LANDING FOUND LARGE LEAK ON #1 BRAKE ON LEFT MLG. HYD FLUID UNDER FUSELAGE. MAINTENANCE FOUND LEAK FROM PTU HP MANIFOLD UPPER REDUCER. REPLACED REDUCER AND O-RING IAW AMM 29-13-15. NO PUMP CAUTION, PERFOMED TSM 29-10-00-810-803-A FOR LOSS OF PRESSURE . ALL CHECKS GOOD, NO LEAKS NOTED.