I wouldn't stress a lot regarding the fin on the bottom, just seal it up so it will not leak. Ironically I welded up a lower unit just two days in the past. Male hit a rock and punched a hole in the front of his unit, dug the chunks https://repair-marine-electronics12593.post-blogs.com/52915764/the-2-minute-rule-for-on-location-lower-unit-repair