How do I know if my rear differential breather is clogged? I took off my rear 3rd two weeks ago and put it back on sealing it with grey RTV took the truck mudding a week ago and new my rear is slowly leaking between the axle housing and 3rd member.

So my question is, would the breather just be glogged forcing the oil out or could I have just done a poor job of sealing? I'd rather not pull my 3rd and find out my seal was fine.

 

go look at your breather. Or whip the oil away, replace the breather and watch. I had two leaky seals front and back on my 85. the front it was the seal, the rear it was the breather. Just look at it.