ACFT EQUIP PROB. LOSS OF OIL PRESSURE; ENG SHUT DOWN AND FLT DIVERTED. RPTR DID NOT DECLARE AN EMER AND LNDG WAS UNEVENTFUL. AN OIL FILTER O-RING WAS TORN AND DISTORTED. AFTER INSTALLING NEW O-RING; ENG RUN-UP AND FILTER CHKED. THE ACFT CONTINUED TO DEST. THE MECH WHO REPLACED THE O- RING DID NOT HAVE THE ENG MANUAL NOR WERE THERE TRAINED PERSONNEL FOR THE SPECIFIC ENG AVAILABLE LOCALLY.

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AT FL370 ON AN IFR FLT PLAN; ABOUT 120 NM W OF EL PASO AND PROCEEDING DIRECT TO ELP; THE L ENG OIL PRESSURE DROPPED TO THE RED LINE AND THEN BELOW. AFTER REVIEWING THE CHKLIST AND MONITORING OIL PRESSURE AND OIL TEMP FOR A MIN OR SO; I SHUT DOWN THE ENG PER THE CHKLIST. I NOTIFIED ZAB THAT I WOULD NEED TO LAND AT EL PASO. AFTER OPPOSITE DIRECTION TFC PASSED BELOW I WAS GIVEN A DSCNT; AND A NORMAL SINGLE-ENG VISUAL APCH AND LNDG ON RWY 22 FOLLOWED. AN EMER WAS NOT DECLARED AND NO ASSISTANCE OR SPECIAL HANDLING WAS REQUESTED. AT THE MAINT FACILITY AT EL PASO; AND VIA SEVERAL TELEPHONE CONSULTATIONS WITH OUR MECH IN AUSTIN AND THE PRATT AND WHITNEY REPRESENTATIVE IN PHOENIX; WE DETERMINED A TROUBLESHOOTING PROC TO BE FOLLOWED. THE L ENG WAS CLEANED AND SVCED WITH OIL AND MOTORED TO CHK FOR LEAKS. THE OIL FILTER O-RING WAS FOUND TO BE TORN AND DISTORTED; ALLOWING OIL LEAKAGE. THE ACCESSORY GEARBOX WAS DRAINED OF OIL AND CHKED WITH A MAGNET. A SLIGHT AMOUNT OF SLUDGE WAS IN THE BOTTOM OF THE GEARBOX CASE; AND NO FERROUS METAL WAS FOUND. THIS WAS CONSIDERED NORMAL AS THE ENG HAS RUN 3454 HRS SINCE NEW. AFTER REMOVING AND CHKING THE FILTER ITSELF; WITH NO FERROUS METAL BEING FOUND; WE REINSTALLED IT WITH A NEW O-RING; AND PERFORMED A 30 MIN GND RUN INCLUDING HIGH PWR CHKS. THE ENG STARTED AND RAN AS NORMAL AND ALL INST INDICATIONS WERE NORMAL. THERE WERE NO OIL LEAKS AND NO UNUSUAL NOISES FROM THE ENG OR ACCESSORIES. UPON COMPLETION OF THE GND RUN THE FILTER WAS AGAIN REMOVED AND EXAMINED WITH NO FERROUS METAL FOUND. AFTER CONSULTING AGAIN WITH BOTH THE MECH AND THE PRATT AND WHITNEY REPRESENTATIVE; IT WAS DETERMINED THAT THE ENG WAS NORMAL IN EVERY WAY. FURTHER TROUBLESHOOTING IN EL PASO WAS NOT INDICATED AND THE SHOP DID NOT HAVE COMPLETE ENG MANUALS OR JT15-TRAINED PERSONNEL. THE PRATT AND WHITNEY REPRESENTATIVE RECOMMENDED THAT AN OIL SAMPLE BE ANALYZED AFTER 10 HRS OF ENG OP; WHICH WILL BE DONE. THE FILTER WAS REINSTALLED; THE ENG SVCED WITH ANOTHER QUART OF OIL; AND THE AIRPLANE WAS BROUGHT TO AUSTIN WITH ALL OPS AND INDICATIONS NORMAL.