This is a subject that has been discussed many times before on the forum, and there are as many opinions as there are replies. Some people believe that water itself is enough lubrication, others prefer various types of oil, and others, like myself, swear by grease. In my case, I always use outboard motor grease which is water resistant and does not emulsify when in contact with water. Some argue that grease puts an additional load on the motor by causing drag on the shaft. In my experience any drag is so minimal as to be inconsequential, particularly in the type of boats I run. It may be a problem with high performance vessels, but all mine are slow running, so any drag is not a factor.
I make all my own prop shaft assemblies, and silver solder a grease tube into the prop shaft tube, with a cap, as shown in the photo below. I use a small syringe to inject the grease into the prop tube, then add grease as necessary my filling the cap and pushing it over the grease tube.
Peter.
