All complete. New seal fitted and working. So it absolutely is serviceable.
Thank you for posting this, I've recently changed the same seal and your pictures were very helpful!
I did find the original seal to be a very peculiar size so opted to try a seal 1mm thicker. As the original one sits within the casting, the new one just sits flush instead.
For anyone else thinking of doing this or having it done, make sure a picture is taken of the selector mechanism before undoing the bolt to remove the shaft! There's some play in the selectors before the bolt is tightened so if not back in the same place could result in gears being in the wrong place or it not going into gear at all. It won't do any harm but will mean taking everything off again to readjust.