As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR INFLIGHT. NOXIOUS ODOR COMING FROM AIR CONDITIONING PACKS DURING DESCENT AND CLIMB-OUT. CREW USED OXYGEN MASKS DUE TO EYE IRRITATION. LANDED LHR WITHOUT INCIDENT. FOUND EVIDENCE OF OIL LEAK ON NR 1 ENGINE CORE AROUND TRANSFER GEARBOX. REPLACED NUMBER ONE ENGINE ON 20 DEC AT DFW. SYSTEM GROUND CHECKED NORMAL OPERATION.