The tube sticks down into the housing a bit MAYBE oil is spinning from the axle and hitting the threaded tube and wicking up?
If the drain was sticking it would build pressure in the housing and maybe erupt??? (but it would also tend to push past the inner seal too???)
I'm reaching for straws!
The older housings had the breather on the side of the hump, the newer ones had it on the tube, my understanding it was to reduce oil blow out. My rear has the older style breather on the side of the hump and a OEM 57 years old breather that I cleaned up. I used Teflon tape on the threads and I have not had any issues.
The FSM says some number of pints, when I drained and refilled my rear after the initial brake in period, I added the number of pints which brought the level over the bottom of the drain plug level. I assume there was a small amount of original oil left in the housing. I also recall that the level should be 1/2 inch below to at the bottom of the drain plug.
