I'm no expert, but I may have an answer. While your FD was immersed and went from hot to cold, a little weeny fish baby (fry) was sucked in past the seal. In the warm tropical environment within the rear drive, its growth rate experienced phenomenal acceleration. This caused a pressure build up due to the space the growing fishy was taking up and explains the 2-3ml of stinky oil flying out. Over the next few days the final drive temps have gotten too high and the fish, who has been swimming madly around inside the final drive avoiding all the moving parts finally reaches its thermal maximum and subsequently expires. Its body is immediately macerated and now starts to decompose within the drive fluid. The subsequent gases given off by this decomposition, mainly methane and sulphur dioxide, cause the seal to start leaking, otherwise your FD would end up looking like a dead cow in a paddock. You drain the rotten fish smelling and containing oil, ,replace with clean oil and the problem goes away. It would be easy enough to replicate this theory, next time you change your FD oil, shove a Fish Finger in as well and go for a trip. I'd try it myself but unfortunately I don't own a 1200. Hope that helps.