Do a search on steering gear seal leakage, then call the local Nissan dealer to inquire about the price of a replacement steering gearbox. I guarantee you'll be selling your Xterra in no time.

Just fanning the flames a little.

Edited to add a couple of issues that have struck me before I switched to Nissan:

Do a Google search on sun gear 4l60e

Or: 3.8 head gasket

Just a couple good reads that should keep one entertained for hours.