AN MD80 LOST OIL QUANTITY BECAUSE OF A REAR OIL SEAL FAILURE. THE CREW DECLARED AN EMER; DIVERTED; AND LANDED WITH THE ENG AT IDLE.

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AFTER LEVEL OFF AT CRUISE FL320; EXPERIENCED A R ENG OIL PRESSURE LOW LIGHT. OTHER ENG READINGS NORMAL EXCEPT FOR ZERO OIL QUANTITY. ACCOMPLISHED CHKLISTS AND DIVERTED TO ZZZZ WITH ENG IN IDLE. ACCOMPLISHED AN OVERWEIGHT LNDG WITH CFR STANDING BY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FO STATED THAT THE ENG WAS INTACT. HOWEVER; THE AFT ENG SECTION WAS SOAKED IN OIL. MAINT DETERMINED THAT THE REAR OIL SEAL FAILED. THE TURBINE SECTION WAS UNDAMAGED. SUPPLEMENTAL INFO FROM ACN 648613: WE HAD JUST LEVELED OFF AT FL320 WHEN THE R OIL PRESS LOW LIGHT ILLUMINATED ON THE OVERHEAD PANEL. WE CHKED THE OTHER INSTRUMENTS AND DETERMINED THAT THE OIL PRESSURE WAS LOW (APPROX 33 PSI) AND THE OIL QUANTITY WAS 0. THE N2 WAS APPROX 68% AND THE OIL TEMP WAS APPROX 96 DEGS CELSIUS. WE FOLLOWED THE EMER CHKLIST PROCS WHILE DSNDING TO A LOWER ALT AND RETARDED THE AFFECTED THROTTLE TO IDLE. WE DECLARED AN EMER AND GOT VECTORS TOWARDS ZZZZ. WE WERE OVERWEIGHT FOR LNDG (136800 LBS AT LNDG) AND DECIDED TO KEEP THE R THROTTLE AT IDLE INSTEAD OF SHUTTING THE ENG DOWN BECAUSE WE STILL HAD N2 AND OIL PRESSURE. AFTER LNDG; WE SHUT THE R ENG DOWN AND TAXIED TO THE GATE WITH THE ARFF EQUIP FOLLOWING US. THE R OIL PRESSURE STAYED ABOVE 20 PSI FOR THE ENTIRE TIME OF THE EMER; WHICH WAS APPROX 20 MINS FROM START TO LNDG AND ENG SHUTDOWN. CALLBACK CONVERSATION WITH RPTR ACN 648613 REVEALED THE FOLLOWING INFO: CAPT STATED THE SAME BASIC FACTS AS THE FO. THE ENG WAS INTACT WITH A VERY SMALL QUANTITY OF OIL REMAINING IN THE OIL TANK AND THE TURBINE SECTION WAS DRIPPING IN OIL.