I sprayed a little brake cleaner on it and poured a few gallons of water to wash it off and it got rid of most of the leaky fluid. Then I realized that when I drive it to him it will leak again since there is still some in the reservoir.

 

Warn hubs are great. I put them on my 2000 and my 2003. Warn at one time had something to do with making hubs for almost all of the truck makers. They are still on my 1972 Chevy gasser that I wished I had back. Also The Warn premiums are guaranteed for life or used to be. I had a very similar issue to yours and remembered that I had some work done on the front and they had not lined up the hub correctly when reassembling so only one side engaged.

 

If you want proper hardcore locking hubs, check out Yukon.