2001 Mercury Mariner 50-60HP Factory Service Manual, Page 467Get this manual
BIGFOOT GEAR HOUSING
Draining and Inspecting Gear Lubricant
WARNING
If gear housing is installed on engine, to avoid accidental starting, disconnect (and isolate) spark plug leads from spark plugs before working near the propeller1With gear housing in normal running position, place clean pan under housing and remove the two vent screws and one filldrain screw (with gaskets)