All or nothing bro.
If you are going to the effort of removing the carrier change BOTH the gasket and the seal, due to their very convenient and easy access......
Sarcasm off, as access requires near total disassembly of the bike and is a hugh PITA, do it once do it right.
While youre in there have a look at the breather gasket and the cam welsh plug as leak points.
If the rear main isnt leaking I agree with the rest of the above posts.
What are you doing thats got you in that deep?