Currie 9” Rear-end

Also, FWIW no one hardly ever thinks about, but depending on WHAT you used in it.......some gear oils and additives do not react well together, I don't care WHAT the labels say. I've see some mixtures sorta "boil over" and force their way out. Course they ain't really "boiling", it's a chemical reaction, but you have to watch what all you mix together. Just thought I'd throw that out there. Either not being vented, OR the vent not working properly I think is a more probable cause.