As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEX/ORD - FLT 5605 - PARKED AT THE GATE IN ORD, FLIGHT ATTENDANT REPORTED CABIN FILLED WITH SMOKE, CFR AT ORD NOTIFIED. REPLACED O-RING ON YELLOW SYSTEM HYDRAULIC PRESSURE FILTER HOUSING. NOTE: CABIN FILLED WITH HYDRAULIC MIST, NOT SMOKE AS REPORTED BY FLIGHT ATTENDANT. (X)