yeah if its your pinion seal leaking you will have to take diff centre out of carrier and remove pinion and the only way to knock the seal out is from the opposite end (being from inside the carrier) and if the flange locking nut is taken off you need to set preload again on the pinion.
not to say you MAY be able to just remove the locking nut and flange and try to get seal out while still all assembled leaving the pinion and diff together, but you might not be able to get preload correct. (not really recomended but let me know if someone has done this)
also when you get the tailshaft flange out check to see if where the seal runs on has made a groove in the flange and if it has, to order a speedy sleeve to cover the groove along with a new seal