Hi all. Well, thanks to your help, I think I've got it licked. It was a bit more involved than I had imagined, in particular removal and refitting of the rear bearing. The output shaft had a visible score line where the seal sat, but you couldn't actually feel it with a nail. It was also slightly corroded, but not where the seal sits. Managed to clean it up ok with some wet and dry and very careful use of a Dremel. The new seal is of a different design and so naturally sits in a different spot, so decided there was no need to sleeve. So far no leaks, but time will tell.
I say no leaks, but actually now there's a different leak, coming from between B2 and B1 on the attached. Am I right in thinking that this just houses a repair kit for the oil pump, and can be removed and resealed independently of the rest of the oil pump assembly?
Thanks 🙂