1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 202Get this manual
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7 Replace second lubricant "Vent" screw and gasketIMPORTANT: Do not lose more than one fluid ounce (30cc) of gear lubricant while reinstalling "FILL" screw8 Remove lubricant tube from "Fill" hole; ins