Mercury - Fill & Drain Screw Kit Gearcase Service Hardware 22-8M0083059. Overview. This fill and drain screw kit replaces the hardware used to open and close the lower-unit gear-lube ports on many Mercury and MerCruiser gearcases. These small screws deal with repeated removal, exposure to heat, saltwater, and vibration, so over time they can round off, lose their sealing ability, or develop corrosion that affects how the gearcase holds pressure. Replacing them as a set keeps the drains sealing p