The pinion seal is one of the easiest problems to fix you don't even have to remove the third member. Just drain the diff, take off the driveshaft, remove the big nut and yoke then pry out the seal. Put in new seal, replace yoke attach and torque the big nut put driveshaft back on and fill with oil. Done. Last one I did took all of 30 minutes and $9.00 for the seal.