the area where the upper casting wears on the lower is aboui .100 deep it seames to have caused the tiller arm to bang a void in the hull.
can the casting be welded?
is their another fix short of new castings.

Never heard of that one. Perhaps Matt Miller could answer that question.
You might send him a private message on this Forum -- he posts a lot on the H16 and the Open Forum.
Just click on his User Name and you will a button to push to send a private message,
Good luck,
Rick