What was found
CREW REPORTED THAT UPON TAKEOFF, AT APPROXIMATELY 400 FEET, CREW BECAME AWARE OF SMOKE IN THE COCKPIT AND CABIN. AFTER LEVELING OFF AT 4000 FEET, THE SMOKE RAPIDLY DISSIPATED AND WENT AWAY WITH POWER REDUCTION AND THE RECIRCULATION FANS TURNED OFF. CREW DECLARED AN EMERGENCY AND RETURNED TO KSDF. THE AIRCRAFT LANDED WITHOUT INCIDENT. UPON LANDING, EMERGENCY PERSONNEL CHECKED THE AIRCRAFT BEFORE RETURNING IT TO THE GATE. MAINTENANCE REPLACED THE ENGINE ONE ZERO CARBON SEAL. OPERATIONAL CHECKS AND LEAK CHECKS WERE GOOD WITH NO FURTHER DEFECTS NOTED.