As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: FLIGHT RETURNED TO LHR ON ACCOUNT OF LOW LEVEL OF YELLOW HYDRAULIC SYSTEM INDICATION. AN EMERGENCY WAS DECLARED AND THE FLIGHT LANDED OVERWEIGHT WITHOUT INCIDENT. MAINTENANCE FOUND A LEAKING T-FITTING DURING TROUBLESHOOTING. REMOVED AND REPLACED T-FITTING IAW AMM 29-13-03. OPS CHECK AND LEAK CHECK GOOD.