It will be hard to patch that crack from the outside because of the gear oil residue that is constantly weeping through it. And yes, the upper gearcase and skeg are matched pieces from the factory and not meant to be interchanged, but plenty of people have done it and gotten away with it. A gamble for sure, I guess I would test it out by assembling the unit “dry” with no sealer to make sure things fit and rotated properly, before going through all the effort of sealing it up..
I would follow Mumbles’ advice if you have access to a talented tech who is good at welding aluminum.. Just make sure the weld bead does not interfere with the rotating gears, seems unlikely but anything is possible.
