What was found
APU DRAIN MAST OBSERVED LEAKING FUEL- APU SECURED -A/C SHUTDOWN LEAK STOPPED. GROUNDED - YES. PERFORMED START UP OF APU AND FOUND PRIMARY FUEL MANIFOLD B-NUT ON THE FUEL NOZZLE AT THE 5 O'CLOCK POSITION LEAKING SIGNIFICANTLY. FOUND B-NUT TO BE SECURE. RE-SECURED ELECTRICAL CONNECTOR TO IGNITION UNIT, REF B737-800 AMM 49-41-31. REMOVED AND REPLACED APU PRIMARY FUEL MANIFOLD ASSY REF AMM 49-31-16-000-801 & 49-31-16-400-801. OPS AND LEAK CHECK GOOD.