B747-200 CREW WAS LOSING OIL FROM #3 ENG IN ZLC CLASS A AIRSPACE.

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ENRTE ZZZ-HNG FL350; SO NOTICED #3 ENG LOSING OIL 1.0 TO 1.5 GPH. SO MONITORED ENG #3 OIL QUANTITY AND IT CONTINUED TO DECREASE. ADVISED COMPANY MAINT CTL. THEY SUGGESTED MONITORING THE ENG CLOSELY. WHEN OIL QUANTITY REACHED ZERO; CREW DECIDED TO LAND AT SAN FRANCISCO AND NOT PROCEED OVERWATER INTO A LIKELY 3-ENG SCENARIO. OIL QUANTITY CONTINUED TO DROP. RECEIVED CLRNC TO DSND TO FL240 AND PROCEED DIRECT SAN FRANCISCO. COORD WITH CABIN CREW TO LAND IN 25-30 MINS. ACFT WT APPROX 600000 LBS. NO FUEL DUMP NECESSARY. DURING DSCNT; SFO APCH CTL DECLARED EMER FOR THE ACFT. CAPT AND FO NOTICED OILY SMELL IN COCKPIT AND FLT ATTENDANT CALLED FORWARD STATING OIL APPEARED TO BE LEAKING ONTO #3 ENG COWL; AND ONTO ACFT WINDOWS ON R SIDE OF ACFT AFT OF WING. CREW IMMEDIATELY REQUESTED EXPEDITED DSCNT AND PRIORITY HANDLING. SO COMMUNICATED THIS UPDATE TO CABIN CREW; INDICATING LNDG WAS NOW 5-10 MINS AWAY. APPROPRIATE CHKLISTS COMPLETED. ACFT CLRED TO; AND ESTABLISHED ON FINAL APCH APPROX 3000-4000 FT AND 8-10 MI FROM ARPT; INSUFFICIENT ALT AND TIME REMAINING TO DUMP FUEL. ACFT MADE VERY SMOOTH AND UNEVENTFUL LNDG; ROLLOUT AND TAXI IN. ACFT LANDED 7000 LBS OVERWT. TAXIED TO GATE. SFO MAINT TROUBLESHOT #3 ENG. COULD NOT DETERMINE SOURCE OF LEAK. MAINT ALSO PERFORMED OVERWT LNDG INSPECTION; AND PRONOUNCED ACFT 'SAFE FOR FLT.' MAINT ISSUED FERRY PERMIT AND MAINT CTL ORDER FOR FERRY FLT BACK TO ZZZ. CREW FERRIED ACFT TO ZZZ. UNEVENTFUL FLT; EXCEPT FOR SLIGHT OIL LOSS ON #3 ENG; ABOUT 1 GPH. SFO APCH HAD DECLARED EMER SIT FOR THE ACFT PRIOR TO APCH AND LNDG BACK AT SFO.