We noticed a small crack in the paint on the bottom of the boat between the saildrive and the rudder. The Scanmar hulls were made of two molds glued together, usually mostly from the inside. The crack appears where the two parts were joined together.
I carved out some of the filler material with a dremel tool, then filled it with thickened epoxy. After it cured, we laid 4 layers of 300g woven fiberglass cloth on it. Finished with 3 layers of 407 fairing compound. It gets two layers of unthickened epoxy as a barrier coat.