What was found
(CAN) THE ENGINE, O/H, WAS INSTALLED & ACFT RETURNED TO SERVICE. DURING THE POST FLIGHT INSPECTION FUEL LEAKAGE WAS NOTICED UNDER THE COWLING. THE GROUND RUN WAS CARRIED OUT & FUEL LEAK, STREAK, WAS OBSERVED ON A BLANKING CAP ON TOP OF THE HMU. A MECHANIC CONFIRMED SAFETY WIRE WAS INSTALLED BUT OBSERVED A CUT O-RING & COULD TIGHTEN IT APPROXIMATELY 1 TURN. HMU WILL BE REPLACED.