xj750 leaking rear hub/dif

So i went out to take my bike today and i notice my rear hub is all yellow and there is a puddle of 80/90weight on the floor. So i traced the leak back to the top of the hub at the cray cap like thing. Its not over filled i filled in the fall thru the hole in the side, and while it was on its center stand. This is my daily driver. So im thinking its gotta be due to the 8 and -5 temps i have been riding in. But this is the first time its done this and it has only been like in the 10's the past 3 days but so idk. pic link below

 

When is cold out, ... the Hypoid gets bunched-up below the breather.
A little bit will get forced-out.

Normal.

 

okay but its been suoer cold for weeks u would think this would have happened already

 

More power to ya for riding in those temps. To prevent this, you'll probably want to switch to synthetic in there.