Why is this bolt near the axle loose?

[2009_Suburban]

This photo is taken under the weel well on the left side of the car. The axle is on the right, and tie rod on the left. I have circled a bolt that is loose. There is a gap between it and the metal it is screwing into. It does not move by hand, and I have not tried tightening with a ratchet yet. I assume this bolt is not supposed to be like that. Why is it coming out? Should I just torque it, and be done with it, or does it need some kind of threadlocker to make it not come out again? If I do need to torque it, how can I get the torque spec?

 

[swathdiver]

That is one of the 2 bolts that secures your front differential to the truck.  It screws into that bracket right above it which in turn bolts to the frame.  The bushings in the bracket above eventually wear out necessitating new brackets.  You can see one of the bracket bolts just to the left in that photo.

 

All that dirt from a leaky seal somewhere tells me it's been a while since you changed the front differential fluid!  Put your hands flat on the table while I grab my ruler!