Another Update.
The gearbox was completely caked in oil, dirt, and American road mess so I got out the pressure washer and started to hose it down. In cleaning it up I came across something quite peculiar. A large hole near the clutch fork. So I decided to disassemble the gearbox to see if anything had come loose but could not see anything so I have no idea where this hole came from.
I am planning to take it to my metal mate who can hopefully weld in a small section of ally to fill and then I will rebuild and spray. Or shall I just look at getting a new housing?
Where do you think this hole came from?
I also noted that the gearbox main shaft has a large amount of play in the arm, only being stopped by the other gear (see the 4 photos) is this normal?