As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, THE TOWER REPORTED THE LEFT ENGINE WAS SMOKING. ALL ENGINE INDICATIONS WERE NORMAL. AIRCRAFT RETURNED TO DTW AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE O-RING ON THE OIL TANK CAP FOR THE LEFT ENGINE AND SERVICED ENGINE. ENGINE OPERATIONAL CHECK OK.