7/70 powertrain?  I think that was still in place for '04?

Okay... but it ain't pretty.  The 'official' way to do it is to remove the
driveshaft (obviously - but mark it's relationship to the pinion flange so
you can put it back the same way), then remove the hub bearings and pull the
axles.  Measure the rotating torque of the pinion nut with an inch-pound
torque wrench (must be a beam or dial type), and record.  Hold the flange
with some type of fixture, and back off the pinion nut (an air impact gun
works best).  Pull the flange out with a puller or slide hammer.  Remove the
seal, and replace with a new one.  Apply a light coat of grease to the seal
lip, and re-install the flange (tap it in lightly, just enough so that you
can catch the threads of the pinion with the nut).  Clean the pinion threads
with brake cleaner, and put a little red Loctite on the threads.  Put the
nut on, and tighten it - then check your rotating torque again.  Continue
tightening, a little at a time, and checking, until you get 3-5 in.lbs. over
your initial reading.  Be sure to spin the flange around, back and forth, to
seat the bearings before reading the torque.

Once that's done, re-install the axle shafts, bearings, etc. etc., and
driveshaft.

Sounds like fun, doesn't it?

I'm a little confused about why you think you can fix it better than
the the dealer and then you how to do it. Then after Tom goes through a
(as usual) generous, lengthy, detailed and accurate how-to, you take it
to the dealer anyway.

You paid for the warranty in the purchase price of the vehicle. Why
would you even think of doing it yourself? Especially since you don't
know how to do it.