Back when I worked at the Triumph dealer, we had a 675 with the output shaft seal leak. When you tried to drive the seal in, it would roll back the rubber coating on the outside of the seal and then of course it will leak. Is this the problem you are having?
If so, what I did was use a bit of emory cloth (sp?) to smooth off the outside lip of the case and gave it a slight bevel. Then I could drive the seal in without damaging the outside sealing surface.
