As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - CREW REPORTED LEFT ENGINE LOW OIL PRESSURE. LEFT ENGINE WAS SHUTDOWN (SINGLE ENGINE TIME 10 MINUTES). EMERGENCY DECLARED FLIGHT RETURNED ORD LANDED WITHOUT INCIDENT. AIRCAFT REMOVED FROM SERVICE. REPLACED FUEL OIL HEAT EXCHANGER THAT WAS LEAKING. SYSTEM GROUND CHECK NORMAL OPERATION.