If the picture is correct, that surface looks unpainted and really pitted. If that's true, there's going to be more spots like you found - the Al will be very thin. Based solely on the picture, it may be time for a new bracket. You don't want to fix a few spots only to have the whole thing crumble while you're out on the water and lose your engine and/or possibly tear a hole in the boat and have the boat sink, too. That's obviously the worst case scenario - but it's a realistic one, as well.