Thanks for the update Paul, I hope this trouble is behind you.
I'm curious; were any other parts changed with the oil seal? Did you ever get more info on their 'special' tool (I've no idea what it could be)?
I do think it would be valuable for you to periodically put your finger in the Centa Bell Housing access hole and check for oil in the rearward area. If oil were to leak again it would first accumulate in this area (downhill from the access hole) before it dripped out.