Mercury - Complete Gearcase Bravo One XR Series Corrosion-Resistant Alloy 8866A82. Overview. There's a certain thrill that comes with running a high-performance sterndrive - that quick lift onto plane, the steady surge as the hull settles in, and the confidence that the boat will respond exactly when you ask it to. But that kind of precision only happens when every part below the waterline is pulling its weight. The Mercury Marine part number 8866A82 Complete Gearcase is built for boaters who ex