Bung is the plug at the stern to release water from hulls.

To use the rudders properly I mean learn their actioan on shore and don't just let them hit the beach and lift arm hoping they will survive. They don't for long.

The elbows for the rudder system are cheap and excellent. You can order them form the Aussie windrush site.
To unload the pressure on the rudders just jam a piece of wood or whatever under the arm after you lift it. This will let the rudders swing.
A piece of strait wire will go through the section while spring is in I think.
(I presume the system is still presusure loaded and it is just the elbow that is missing)

You could refer to your manual to imagine what you are having to do blind.
Elecrical tape is good to secure and new line with and the wire will drag that through.
Use a ball end once fitted and with the rudder in down position the ball should be almost tight to elbow.

The rudders have three positions that with a little practice are easily gaged ofr leaving and arriving.
The system works very well once mastered and is the only one with which I bother to raise the windward blade.