As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INBOUND TO O-HARE, HYDRAULIC FLUID LOSS DOWN TO ONE GALLON. A-SYSTEM PUMPS DEPRESSURIZED BEFORE LOW PRESSURE LIGHTS ILLUMINATED. LANDED WITHOUT FURTHER INCIDENT. FOUND THE A-SYSTEM HYDRAULIC PRESSURE TRANSMITTER LEAKING. REPLACED THE HYDRAULIC LINE THAT GOES TO TRANSMITTER. CHECKED FOR LEAKS AND NO LEAKS NOTED.