Also, read this thread for a DIY tool to INSTALL the new axle seals:http://www.jkowners.com/forum/showthread.php?p=425844
The seals cost about $25 at the Jeep dealership.
When you re-install the axle shafts, be sure to put a glob of grease on the ends of the shafts (on the threaded ends going into the diff) to protect the new seals from getting shredded.
DIY, takes about 2-3 hours. And DON'T forget to add new differential fluid when done!!!
If you have sleeves inside the axle, it gets a little more complicated. I can't get my seals removed. I think Jeep welded mine in. D'oh! Taking it to the guy who did my gears to have him replace the seals. That took about 3 hours of frustration to realize this.