As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CREW OBSERVED ECAM MESSAGE BLUE HYDRAULIC SYSTEM LOW QUANTITY. THE CREW DEPRESSURIZED THE HYDRAULIC SYSTEM AS A PRECAUTION. THERE WAS NO LOSS OF HYDRAULIC PRESSURE PRIOR TO CREW ACTION. MAINTENANCE TROUBLE SHOOTING REVEALED THE O RING OF THE SAMPLING VALVE ON THE BLUE HIGH PRESSURE HYDRAULIC SYSTEM MANIFOLD WAS LEAKING. IPC 29-12-03-2 ITEM 130. THE O RING WAS REPLACED AND THE HYDRAULIC SYSTEM REPLENISHED. THE AIRCRAFT RETURNED TO SERVICE.