I wouldn't worry a lot of with regard to the fin on The underside, just seal it up so it does not leak. Ironically I welded up a lower unit just two times in the past. Male strike a rock and punched a hole inside the entrance of his unit, https://archeribrjq.blogthisbiz.com/38008844/helping-the-others-realize-the-advantages-of-on-location-lower-unit-repair