Damn - you've covered a lot the typical misses.
Bit of a Hail Mary here: You sure it's the hub? Given where it's coming from, you may be leaking hydraulic fluid from the wheel cylinder...
I've misidentified this same leak from the same location... In my case it was the reverse. I thought the leak was the wheel cylinder - but it was the hub that was leaking (my distance piece/race was corroded and would quickly compromise the seal's lip).
Easy way to check is to pull back the rubber covers at the ends of the cylinder and see if there is fluid in there.
1968 Series IIa
1997 Defender SW (Original Owner - Sold)