What was found
PILOT STARTED ENGINE, COMPLETED CHECKLIST AND (BEEPS) IN HEADSET AND VISUAL WARNING ON CAUTION PANEL OF MAIN GEAR BOX (LOW OIL PRESSURE). SHUT DOWN ENGINE AND OPENED COWL, TRANSMISSION FILLED WAS COVERING BOTH ENGINE DECK AND TRANSMISSION DECK. DISCOVERED THAT THE BLANKING PLUG HAD COME LOOSE FROM TRANS INPUT FLANGE CAUSING LOSS OF TRANS FLUID. THIS (LOOSE BLANKING PLUG) ADDRESSED IN ALERT SB 63-003, WHEN THIS EVENT HAPPENS IT IS NOT JUST A SMALL LEAK WITH MINOR CONSEQUENCES, BUT A MAJOR LEAK, EMPTYING THE TRANSMISSION WITHIN A SHORT PERIOD CAUSING A POWER REDUCTION IAW FLIGHT MANUAL, A RUN ON LANDING, OR POSSIBLE CRASH.