Something is Wet in my rear wheel.

x2 but I didn't do the diff breather.

 

I had the VERY sam problem, only on BOTH sides. You have two seals on either side. The inner seal is easily replaceable, the outter seal requires you to change the bearings when you replace the seal. I went and picked up two inner seals, two outer seals, and two bearings. It's cheap and easy to replace, just tedious. After replacing the seals and bearings, you should redo your axel fluid, in case it's low due to the leaking, and put additive in the diff for your locker.

 

Unless the bearings are bad then you just need to worry about the inner seals. The outer seals just act as a barrier for mud, dirt, etc. They won't stop oil from passing through.