Antique outboard collectors like myself use Lubriplate 105 assembly grease in the lower units of outboard motors. It is a Grade 0 grease. John Deere Corn Head grease has the same lubricity (viscosity ?) rating. Some people fill lower units with it.
I only restore the Mercury automatic transmission outboards made from 1957 - 1962. I squeeze an entire tube of the 105 into the lower unit and the grease finally exits a vent above the propeller about a foot ensuring that the clutch springs, planetary gears and transmission trunion are lubricated.