What was found
FRK - AFTER 2.5 HOURS OF FLIGHT NR 1 ENGINE OIL QTY SHOWED A DROP OF APPROXIMATELY 1 QT PER 20 MINUTES OF FLT. ON APPROACH QTY DROPPED TO 2QT AND PRESSURE STARTED FLUCTUATING 45 PLUG/MINUS 5 PSI. NR 1 ENGINE WAS SHUT DOWN AND SECURED. TROUBLESHOT NR 1 ENGINE OIL SYSTEM FOUND NR 1 ENGINE CSD DRIVE SHAFT O-RING BROKEN. REPLACED WITH SAME. OPS CHECK SATISFACTORY ON ENGINE HIGH POWER FOR 30 MINUTES. (M)