If I read your post correctly you are unsure where the leak is located, but are thinking the rudder post area. Two things if in the leak is really in the rudder post area:
- Have you checked and or replaced your rudder packing?
- Most older rudder shafts are supported in a post made of wood (normally enclosed in resin/FRP) which can eventually rot out and start leaking. Complete replacement by a competent yard is required.
A crack in the hull was also mentioned - you "fix that." Could you elaborate on how you fixed that and where was the crack? This is another case for a good yard with FRP skills to look at.