methods to prevent water intrusion

What are the recommend methods to prevent water intrusion at the rudder post? Water intrusion into my hull is occurring at the rudder post is getting worst over time. I currently been using Vaseline around the rudder post as a lubricant and leak prevention.

Maybe try this.

Using a dropper or a drinking straw, apply some liquid epoxy (without thickeners) to the rudder post and let it run down to the join with the hull. If it possible to to this on both sides, great. If not - because of access problems, then you will need to move the hull around at different angles to try and get the liquid epoxy to run all around.

Of course if you have good access to the rudder post via a hatch, then you will not need to use a tool like a drinking straw.

How about a piece of rubber tube (model aircraft fuel tubing) which fits over the rudder shaft and over the brass rudder tube.
It could be glued to the rudder tube with cyno.
Well lubed with vasaline or whatever it will prevent water squirting in.

The biggest thing is to have the top of the rudder tube higher than the water line, or as high a possible, but not too much higher than the top of the rudder servo. You may need some kind of support for the tube. Also make sure to have a close-fitting tube and shaft.

The pressure of the water is forcing it up the shaft, even though you have it greased.

Perhaps I misread the question. I have assumed that the problem is at the point the rudder tube joins the hull at its base, i.e. below the waterline.