We decided the best solution would be to build a new wooden rudder.
We are building the rudder of hard mahogany boards. The trick is to drill it for long bolts, which give strength to the structure. The nuts, embedded in the boards, should not be tight, to allow space for the boards to swell when they are wet.
While wooden rudders seem old-fashioned, they actually are perfectly fine. Fiberglass rudders are more common these days, but they have their own problems -- water penetration that can result in freezing and expansion and cracking in the winter as well as crevice corrosion of internal stainless steel parts, especially welds. In the long run, a good wooden rudder with bronze hardware might prove to be more durable than a fiberglass rudder.