Mercury - Complete Gearcase Bravo Three / Three X Series Corrosion-Resistant Alloy 8M0046733. Overview. If you run a Bravo Three drive, you already know how much trust you place in the gearcase. It's doing the hard work every time you ease into gear, trim up onto plane, or push through a tight turn with a crosswind. When a gearcase starts to fail, you feel it in your gut long before you hear it. That is why boaters who demand reliability turn to the Mercury 8M0046733 Complete Gearcase. It brings