Changing the Gear lube in you Sterndrive or Outboard lower unit is a routine maintenance that should be performed every 100hrs of use or annually, which ever comes first. All mechanical shift models are recommended to use a Synthetic Blend gear lube for better lubrication and cooling protection. The standard 80W90 gear lube is still available for use as well a gear lubes for electric shift units. Be sure to use the best proper gear lube for your application.