"if this problem exists on models manufactured prior to this date, which do not have a second drilling in the oil spray nozzle for the oil supply of the piston vacuum pump, or for performing work which requires taking off the vacuum pump, remove the centering sleeve and install in modified seal for improving the oil supply." -
PR 07.1.1064 /6
What is this centering sleeve and does it exist in any M/Y 1987 603 engines? The "modified seal" is the gasket with the dam across the bottom.