1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 321Get this manual
Screw in vacuum testerPump out to 76-127 mm (3"-5") of mercury and see if vacuum holdsThen pump out to 381 mm (15") of mercury and checkIf the gearcase fails to hold on either test, put oil around suspected sealI leak then stops or oil is drawn in, that seal is defectiveWhen the gearcase checks out OK, refill with the proper lubricant 1841