I do not think it is necessary to pull the manifold and turbine to replace those seals... I do not think you even HAVE to pull the lower pan.... although I think that makes it easier to get a good fix... ( if you don't count all the work of pulling the lower pan ) ....
Do a search... I think people have described doing it with things in place... two bolts at the top holding one gasket, one ring in the middle and the one going into the pan...