What was found
CREW REPORTED THAT RT ENGINE OIL LOW PRESSURE ANNUNCIATOR HAD ILLUMINATED WHILE IN CRUISE FLIGHT APPROX AN HOUR AND A HALF AFTER TAKE OFF. RT ENGINE OIL PRESSURE INDICATED BETWEEN 38 - 25 PSI. POWER TO RT ENGINE WAS REDUCED TO FLIGHT IDLE, AND AN EMERGENCY WAS DECLARED. AC LANDED WITHOUT FURTHER INCIDENT. MAINT DISCOVERED A LOOSE BOLT AT NR 6 ENGINE BEARING OIL RETURN LINE. THE OIL LINE WAS REMOVED AND REINSTALLED WITH A NEW GASKET. THE NR 6 BEARING OIL PRESSURE LINE AND N1 TRANSDUCER COVER PLATE WERE RESEALED. THE ENGINE OIL WAS SERVICED AND A SATISFACTORY OPERATIONAL AND LEAK CHECK WAS PERFORMED. THE AIRCRAFT WAS RETURNED TO SERVICE.