As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SMF - CREW REPORTED SMOKE IN COCKPIT AND THEN CABIN. EMERGENCY DECLARED FLIGHT RETURNED SMF LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND AUXILIARY POWER UNIT OIL COOLER LINE LEAKING. REPLACED O-RING ON THE APU OIL COOLER. SYSTEM GROUND CHECK NORMAL OPERATION.