Thats what we call "Birfield Soup". You need to rebuild them
And looks and tastes better then split pea soup.
![Regurgitate! :reg:](https://board.marlincrawler.com/Smileys/marlin/reg.gif)
Usually when they start to leak or the inside looks like oil then the axle seal is bad. Or what I'm guessing you're calling a differential output shaft seals.