I have 1/2 inch irregular hole in aluminum hull, 1976 Starcraft I/O. It appears to be corrosion or damage spot on transom below water line. It is in line with end of stringer, backed by plywood of transom, not very accessible from inside. Surrounding metal seems sound, but I am reluctant to enlarge hole to find out until I have idea how to proceed. Could use safe temporary fix while I decide whether to repower this boat. (Just now got it running enough to put in water.) Weld? Goop? Bolt on patch? Thanks.