As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 893 BOS-STI, CREW DECLARED AN EMERGENCY DUE TO HYD Y RESERVOIR LO LEVEL ECAM APPEARED AT FL200, CONFIRMED HYD PAGE. FOUND LEAK AROUND NR 2 ENG CHECK VALVE AT YELLOW HYDRAULIC PUMP DELIVERY CHECK VALVE. REMOVED AND REPLACED O-RING AT NR 2 ENGINE CHECK VALVE PER 29-13-36-000-001-A. OPS CHECK GOOD.