In 50 years of working on cars, probably twice I have seen a bore for the seal not centered on the shaft protruding through it. It should never happen, but on a couple of rare occasions I have seen the bore off center. This allows one side of the seal to be too tight on the companion flange, and the other side to be not touching it and no matter how many seals you install, it still leaks.
You might try using a seal sleeve on the companion flange to enlarge the OD where the seal rides as there is no real repair to fix the housing if it's bored off center.
I may be completely wrong with this guess, but I have seen it before, something else to try because you' look like you covered all the bases already.
Good luck on your repairs.
__________________
Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix
100% Pontiacs in my driveway!!! What's in your driveway?
If you don't take some of the RACETRACK home with you, Ya got cheated 
  
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