Looks similar to the arrangement of the rudder tube on my NC43. I had a special tool made to release the nuts. The chances are that the packing is OK but needs greasing. If you can clean up all the corrosion, you should find a grease nipple. Try pumping full of thick waterproof grease ( darglow engineering can supply). If this doesn’t seal it, then you need to tighten the nuts down, which means releasing the lower lock nut and then tightening the top nut. For me, this was not trivial, as the clearance is awkward and the nuts were very tight. Very happy to lend you my spanners: they are in Portsmouth but I am not there until early September now. Let me know.