I'm installing the GT500/Boss style rear differential cover on my first rear gear change this weekend, as I like the idea of it having a drain and fill plug on its back cover side for easier access to fill and future drain ease.
I noticed the cover came with a valve of sorts that screws in on the top right, which appears to allow the rear differential case to breathe?

The stock cover I have now does not have this, so I assume the rear differential breathes a different way?

With my older Ford truck, it has a tube that points up and has a U shape at the top; figured this was so it could breathe, and not get water into it, keeping the rear end out of harms way when 4 wheeling.

So, where is the stock breather of sorts for the rear end? Does this need to be capped when I install the new cover that has a valve on its top?

 

Stock breather is on top of the passenger side of the axle housing. The frpp kit I believe plugs the stock breather and moves it to the top of the cover.

Can't see an issue with the breather in either place ...

 

I did not get a plug to cap off the stock breather; I'll leave that as it is and also use the one they provided for the FRPP cover as well. Thanks for the info.