What was found
(CAN) CREW REPORTED, NR 1 ENG OIL PRESSURE WAS BELOW RED AND INDICATION WAS READING ZERO. ENG WAS SHUTDOWN, AC LANDED W/O INCIDENT. MAINT FOUND NR 1 ENG OIL FILTER CAP WAS DISLODGED DUE TO LWR STUDS OF GB HSG HELICOILS FAILING. ENGINEERING ISSUED A PROD PERMIT B737-72-18790 TO REINSTALL HELICOIL WITH REPEAT INSP OF 50 HOURS. HISTORY REVIEWED THAT 2 DAYS PRIOR, THIS OCCURRENCE WAS A REPORT OF AN OIL LEAK FROM NR 1 ENG WHICH WAS NOT EVIDENT DURING ENG RUN AND WAS RELEASED AS GROUND CHECKED SERVICEABLE. AS IT APPEARS THAT OVER TIGHTENING OF THE OIL FILTER CAP NUTS MAY CONTRIBUTE TO PROBLEM, REMINDER ISSUED TO LINE ENGINEERS THAT TORQUE ON THESE FASTENERS IN 25-30 INCH POUNDS AS STATED IN WORK CARD 1193.