Leak With Unknown Source

I've found a strange leak at the rear of my gas tank. It seems to originating from the fitting in the attached photo, but that is part of the charcoal filter system which shouldn't have any fluid in it to begin with. The liquid is like watered-down motor oil and is sprayed all over the diff and axle housing to the right of the fitting, as well as the underside of the bed and all surrounding lines. Any ideas on what the cause might be?

 

U Joint

 

Is the splatter in a straight line? If so this is an option. But sounds like a lot for grease. Also it would have to be pretty thin/watery

Op more pictures would be good too!

 

I'd say U-joint as well because the bolt in the back also looks shiny. When was the last time you had your u-joints serviced?

-J

 

Pinion seal seems possible too.