1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 315Get this manual
3A leak path is created between the UP side of the cylinder and the reservoir when the spool sticks holding the pilot valve open 6Inspect for nicked, deteriorated, or misplaced O-ring
CylinderManifold Mating Surface O-ring Spool Return Spring Valve Seat Pilot Valve Held Open (away from valve seat)
4Power trim units with date code 23289 and higher have improved o-rings and improved surface finish on the inside of the sleeve to correct the problem5To correct slow leak down, check for debris between the valve seat and valvea Valve and Seat O-ring O-ring Scribe Mark