Try replacing just the big seal first. Clean everything well before doing anything.
No gaskets needed, but be careful prying that sucker out. Once it's out, check the seal lip and the surface it rides on for grooves. If there's a groove, you can drive the new seal in slightly deeper or less deep to put the lip on a non-grooved surface.
If you need to replace the big flange gasket, get two. I think there are shims in there between the case and the flange to set the ring and pinion lash. See #24 and #25 here: