As stated above, be sure to buy the actual seal and I recommned the dust-cover from Nissan/Infinty dealer.
http://www.nissanpartszone.com/componen ... -1273.html Shows the pathfinder equivalint parts, under $20 for both.
If your not comfortable with doing the work yourself, source out a muffer/transmission shop for labor quotes as this really should be straightforward job under a hour.
If your going to do it yourself, just be sure to use wheel chocks and parking brake as the transmission "P" does not help much once you discconect the shaft. Also if doing this yourself, put some cardboard down under the front part as you don't want that end to fall and hit pavement when your pulling it out. Plus some fluid likely will drip,