Your pinion seals are pretty easy to change. First drop your drive shaft , then hold the yoke with a pipe wrench and remove the pinion nut. The nut will be torques to around 400 ftlbs, so it might be hard to get off. A two jaw puller might make getting the yoke off easier, but a hammer will work if you don't have a puller. Next, pull out the old seal and drive in the new one. A large socket works well for driving in the new seal. After the seal is fully seated, just slide the yoke back on and reinstall the nut. Some people recommend using a new nut, but I have never had a problem using the old nut. Torque the nut as much as you can, and put your drive shaft back up. You do not need a new yoke, but you may want to clean up the old one at the sealing surface before you re-install it.
Hope that helps.
Mark