What was found
(CAN) WHILE CLIMBING OUT, NOTICED ENG NR 1 OIL QUANTITY INDICATOR SLOWLY DECREASING, QUANTITY WAS 1 GALLON AT TOP OF CLIMB. AT MID POINT, QUANTITY DECREASED TOWARD ZERO. ENGINE SHUTDOWN DRILL AND CHECK LIST COMPLETED. ENGINE WINDMILLING SUPPLEMENT COMPLETED PRIOR TO DESCENT. ALL OTHER ENGINE INDICATIONS NORMAL PRIOR TO SHUTDOWN. OPENED COWLING ON NR 1 ENG, CHECKED FOR OIL LEAK, NOTHING OBVIOUS, ADDED 12 QUARTS OF OIL IAW MM 12-13-001-2. NR 1 ENG RUN AT IDLE TO LEAK CHECK, SIGNIFICANT OIL LEAK FROM GEARBOX TO OIL COOLER TUBE. FOUND OIL LINE HAD TENSION ON IT WHEN REMOVING TUBE. SEAL SPLIT AND REAR PIECE MISSING. PROCURED SEAL P/N 443330 (REV.A). CPN 0043234 INSTALLED SEAL AND REPOSITIONED TUBE, REMOVED PRE-LOAD IAW MM 79-20-001-4. NR 1 ENG GROUND RUN AT IDLE FOR LEAK CHECK, NO LEAKS, NR 1 ENG. COWLED. ACFT OK TO CONTINUE.