Dead end vac. line on '00 D30?

I'm trying to figure out why there is a vac. line coming of my front D30 and up into the engine bay and dead ending right where the hood and firewall meet. I looks like it has a vent of some kind on the hood side. What is this for.

The reason I ask is that the straps holding it to the upper control arm broke and it is now resting against the front yoke and has worn a hole in it and the heat wrap that was on it.

Sounds like a diff vent to me. Fix it so your diff doesnt fill up with water. Thats bad.

Yeah thats the diff vent hose, replace it.

X3 diff vent line

X4 definitely the diff vent