What was found
FLT DIVERTED DUE TO SMOKE IN CABIN. ENGINE REMOVED AND NR 1, 2&3, NR 3 FORWARD & NR 3 AFT CARBON SEALS ALL REMOVED AND CHECKED. ALL CARBON SEALS CHECKED GOOD, MATING SURFACES OF SEAL SEATS OF NR 3 FWD & NR 3 AFT WERE FOUND TO HAVE HEAT CRACKS. MICROCRACKS ARE TYPICAL OF SEAL SEATS & ALTHOUGH THEY PRESSURE TESTED GOOD, STILL HAVE CONTRIBUTED TO SLIGHT LEAKAGE. IN ADDITION, SEAL SEATS ALSO FOUND TO BE SLIGHTLY OUT OF SPEC FOR FLATNESS. COMBINATION OF INCONTIGUOUS FLATNESS & MICROCRACKS IS BELIEVED TO HAVE CAUSED THE INTERMITTANT SEAPAGE OF OIL INTO GAS PATH.