I've installed three 9" Ford rear ends in my cars. The inboard seals never really worked for me. Since the bearing is sealed, a press fit on the axle, and a tight fit in the axle, I just coated the bearing seating area with hi-temp black silicone and tapped the axle into place. None of those three leaked. I'm doing the same with my fourth. Since the axle housing is vented, I've also siliconed between the bearing retainer flange and the axle housing.

It worked for me . . . your mileage may differ.