What type of lower unit gear lube for 90hp mercury two stroke outboard?

For a 90hp Mercury two-stroke outboard, you should use a high-quality lower unit gear lube specifically designed for outboard motors. Mercury recommends using their own brand of gear lube, such as Mercury High-Performance Gear Lube or Quicksilver Gear Lube, which offer Excellent protection against wear and corrosion. Always check the owner's manual for specific recommendations regarding viscosity and any additional requirements.