Mercury - Quicksilver 85W-90 Extreme Performance Gear Lube, 1 Gallon Gearcase Lubrication 92-8M0111679. Overview. High-performance gearcases don't get an easy life. Long wide-open runs, heavy loads, sudden throttle changes-those gears see everything. When you're running equipment that hard, ordinary gear oil just doesn't cut it. This Quicksilver 85W-90 blend is the stuff mechanics use when they know a gearcase is going to be punished. It hangs onto the teeth, stays thick when the drive gets hot,