What was found
(CAN) ACFT MAIN ROTOR TRANSMISSION LOW OIL PRESSURE LIGHT ILLUMINATED IN FLIGHT & PILOT PERFORMED AN UNSCHEDULED LANDING. UPON INSPECTION BY A MECHANIC METAL WAS FOUND ON THE M/R TRANSMISSION CHIP PLUGS. CHIP LIGHT DID NOT ILLUMINATE. TRANSMISSION, PN 369D25100-507 WAS REPLACED & SENT TO COMPONENT DEPARTMENT. DURING TRANSMISSION DISASSEMBLY THE O/P GEAR, PN 369D25127-11, SN 005304-2082 WAS FOUND TO HAVE A TOOTH BROKEN OFF. DURING FURTHER DISASSEMBLY, IT WAS DISCOVERED THAT THE LUBRICATION PUMP DRIVE SHAFT HAD SHEARED OFF DUE TO A PIECE OF THE GEAR TOOTH GOING THROUGH THE PUMP GEAR. THE INOPERATIVE PUMP IS WHAT CAUSED THE LOW OIL PRESSURE LIGHT TO ILLUMINATE.