"Sweating" around rear differential?

[RyanbabZ71]

Ok i have noticed quite a few times there seems to be a noticable ring kinda like the rear diff is sweating all around the outside of the rear diff.  You can see it on the rear axle too.  Nothing is leaking and i have noticed this for a long time now.  Anyone else have this or know what causes it?

[Shaners]

If I had a guess it would be caused by rear-end heat plus high humidity.  As the rear cools the humidity will condense and cause moisture droplets.

[RyanbabZ71]

ill have to take some pics

 

Its not liquid droplets.  

 

Its like (ok this is gross but sorry) if you are sweating and you lift up your arm and you see a sweat ring around your pit