rare front differential oil leak

[vidvis]

I have done that IRA51 - about 6 times in the last couple weeks. I have little doubt I am looking at gear oil. I spray the whole area down with brake parts cleaner after each inspection to clean it all up, let it dry over night, inspect the next morning to ensure it is still clean, then drive it a short distance. When I get back home again, I get the results shown in the pics along with traces of oil splattered onto the frame in that area.

I was hoping this would be something simple like a leaking vent tube or a drip from something else, but can't find the source.

If it is leaking from the seal, the complete lack of any trace of oil on the face of the flange, as would be expected as it leaked from the seal and ran down, and only seeing oil on the outside perimeter has got me baffled.