Full Size Jeep Network

Hi, I'm new to the site and to FSJ ownership. I just picked up an 85 GW. Most everything is great, but the steering box is leaking oil and my steering is very sloppy/loose/sticky etc.

Questions are:
1. best place to buy an inexpensive replacement?
2. how hard/easy is it to replace it myself? (I'm pretty mechanical)

Also, any other words of advice would be greatly appreciated