You need to be cautious with pinion seal replacement. Lots of people just remove the pinion nut with an impact, pull the yoke, pry out the old seal, drive in a new seal, install the yoke and nut then tighten the daylights out of it with an impact.
That is a disaster waiting to happen with any rear end with a pinion bearing crush sleeve(like a 9"). There are two different ways pinion bearing preload is set. First way is with shims between the two inner opposing bearing races, most Dana axles are this type, the second is with a crush sleeve between the two opposing bearing races. With the crush sleeve type the more you tighten the pinion nut the more pinion bearing preload you have. Too little or too much bearing preload spells bearing failure. With a shim style setup pinion seal replacement is easy, because tightening the pinion nut after seal replacement does not change preload. Changing a seal on a crush sleeve setup is a real pain. First you should pull the whole pinion assembly out of the front of the 9" 3rd member, then get a dial inch pound torque wrench and see how many inch pounds it takes to turn your pinion. After you record that remove the pinion nut and yoke. Next replace the seal, then install the yoke and pinion nut. Then it gets tricky, you want to tighten the pinion nut until the torque it takes to turn the pinion is a few inch pounds higher then when you took it apart. If you screw up and go too far you have to pull the whole assembly apart, install a new crush sleeve and try again.
So many mechanics don't understand this and end up destroying pinion bearings. Stock 9" axles have crush sleeve type pinion preload setup.