Rear-end seal?

The only hard part about it is getting the nut loose so you can remove the pinion yoke. I've done it with a breaker bar and a length of cheater pipe with the parking brake set. Once the yoke is off it is just a matter of pulling the old seal out and driving in a new one. Takes maybe 45 minutes with hand tools, half that with air. Sometimes they will leak if the pinion yoke has a groove worn in it where the seal rides. If that's the way yours is, plan on a new yoke.