I finished replacing the seal on the weekend. The socket that is needed is a 30mm deep 12 point socket. I could not use the chisel to mark the shaft that comes out of the differential. (Maybe my chisel was too cheap.)
I ended up using a grinding tool and made a small notch to mark the relationship between the shaft and the nut. Once you feel is start to get snug, all you have to do is take the socket off and make small movements till the marks line up.
I hope this helps someone and thanks for the pointers stevebfl.