Mercury - Gear Lube Pump Lower Unit Service Tool 91-802891A1. Overview. This Mercury gear lube pump makes lower unit service a lot less messy and a whole lot more predictable. It threads right into a standard drain plug port, letting you push fresh lube straight from the bottle without juggling funnels or hoses. It's a simple tool, but it saves time every season-especially when you're doing back-to-back services on multiple motors. Most boaters end up keeping one in their kit because it's depend