What was found
DEFECT- OIL NOTICED ON TAILBOOM AND VERT FIN AFTER SHUTDOWN. NO SECONDARY INDICATIONS NOTED (IE CAUTION, TEMP, OR PRESSURE). MGB SERVICED WITH 3 LITRES OF BP 2380 OIL AND OIL SYS DRAIN LINES DISCONNECTED FOR TROUBLESHOOTING AS NO OIL WAS FOUND ON DECK PANS. ACFT GROUND RAN C/O AND FOUND THAT ALL, PARTICULARLY THE PRESSURE SIDE LINE DUMP VALVE, LEAKS SLIGHTLY WHILE MANIPULATED WITHIN THE STOP INDENT POSITION. ALL 4 VALVE TAP HANDLES LOCKWIRED TO THE HARD OFF POSITION. GRD RUN AND LEAK CHECK FOR 15 MIN. C/O SATISFACTORY. VERIFIED MGB OIL LEVELS. A/C RTS. VERIFIED NO FURTHER LEAKS AFTER A 30 MINIUTE FLIGHT.