[fox46]

I am not familiar with these gearboxes but could you remove the components from the box, assemble the two pieces and pin them together with a 1/16" roll pin or hardened dowel? It appears you wouldn't need anything too substantial since all the torque is carried by the hex but a pinned connection would guarantee it wouldn't release. If that stub shaft is driving anything with a side load, the slightest play or flex in the material will almost guarantee that it will eventually wiggle out of its hole. Make sure you use the "green" locktite retaining compound 680 or similar, not the threadlocker types. JB weld could also be a wise choice. I would imagine the brittle nature of superglues (cyanoacrylates) would crack and debond.