Not hard at all. I've done quite a few of them. After disconnecting the driveshaft, I like to scribe a reference line on the end of the pinion, across the nut, onto the washer onto the yoke. That way you have an idea of where everything was to begin with. Then I use a torque wrench to get a close reading of how tight the nut it currently. Then I take the nut off and change the seal. Pretty easy to pry out and then tap back in. If you have a large socket the same diameter of the seal, it will go easier. Then put it back together with the lines matching up. If the nut it getting tight as you approach lining up with the scibe marks your real good. Just go slightly more and your good to go.