What was found
SMOKE WAS NOTICED AFTER TAKEOFF AND GREW WORSE DURING CLIMB. THE CABIN APPEARED TO HAVE A SIGNIFICANT AMOUNT OF SMOKE AND THE MEDICS NOTIFIED US THAT IT WAS VERY HOT IN THE BACK. WENT THROUGH THE MEMORY ITEMS AND RAN THE SMOKE IN THE COCKPIT CHECKLIST, DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE. MAINTENANCE INSPECTED, RAN AND OPERATIONALLY CHECK MULTIPLE AIRCRAFT SYSTEMS AND HAVE ISOLATED THE PROBLEM TO THE RT ENGINE. IT WAS DETERMINED THE LT ENGINE HAD AN INTERNAL CARBON SEAL LEAKING OIL REPLACEED THE NR 4 & 5 SEALS. MAINTENANCE REPLACED THE LT ENGINE, PERFORMED MULTIPLE SUCCESSFUL GROUND RUNS AND A SATISFACTORY OPERATIONAL CHECK FLIGHT.