Well, waddya know, I have a service manual on that gearcase. You are correct, the skeg has to come off and the innards shucked out to replace the prop shaft seal. The seal comes out of the inner side of the seal housing, and the seal housing is located in place by a dowel pin. So, obviously, several areas of possible leaks exist if not assembled correctly.
(Not bragging either) but I had been working on motors for 4 years when that motor came out. Dang, I feel older than rocks.