Dont know about Bene, but typically the rudder post would have 2 or 3 SS plates (1/4" or so) welded to it extending into the rudder cavity. You might be able to build the post/plates assembly, Then remove your rudder and cut and peel off the fiberglass
shell and reuse it. Or you could use the old shell to layup
a new (albeit slightly larger) shell onto that old rudder. Or you could use that shell as a mold
a new rudder. At any rate, you have to decide what to fill the rudder with. Usually filled with lightweight foam which eventually fills with water
. You could use casting resin and micro ballons ( i did this once) to fill it and avoid water
saturation. It's a little heavier though if you race
. (although not too heavy in water!) If the old rudder post is bent, how do you intend to reuse it?