The casting has been bent, likely by backing the boat onto the beach with a rudder down. This is a common problem with these and probably other boats. Castings fatigue easily; it only takes a couple of bends to break them. We know it's already been bent at least once. The next bend may or may not break it. To be safe, just shim it up so it's tight again.

Whatever you do, do not attempt to bend it by heating! That only works with steel!

Jimbo