What was found
ENGINE OIL PRESSURE LOSS RESULTED FROM DISTORTION OF THE DRAIN VALVE SEALING RING WITHIN THE OIL FILTER ASSEMBLY. INDENTATIONS ON THE SEALING RING CORRESPONDING TO HOLES IN THE FILTER BASE BECAME MISALIGNED DURING FILTER ELEMENT INSPECTION AND FAILED TO PRESENT A FLAT REGISTER TO THE FILTER BASE. THE INDENTATIONS MAY BE ASSOCIATED WITH OVER-TIGHTENING OF THE FILTER BOLT DURING PRIOR MAINTENANCE. THE SEALING RING IS NOT NORMALLY REPLACED DURING OIL FILTER ELEMENT INSPECTION OR REPLACEMENT.