Differential sweat

[dazza]

Can anybody give me some insight on the concave indents, four on each side, of the front diff.? I would assume they're pressed in to hold the axle housing.
The reason I ask is that they all seemed to be filled in with some type of epoxy/weld from the factory, however one is completely smooth like the filler has fallen out. The diff has been empty for over a year now with the cover on, but this one empty indent seems to sweat oil, very slow. I can wipe it and a few days or a week later I'll check it and it will have the oily film.
Should it be filled? With what?

Thanks


The sweaty one:



Wiped clean:



The opposite side of the diff:



Here you can see the one above it, partially filled, no sweat: