So I went ahead and tossed a replacement National/FM 8515N piece in there. What I did notice is that the seal 'housing' (if you can call it that) on the 8515N piece is actually about 1/4" deeper. I'm talking about the metal seal housing which actually presses into the gear housing. What I missed is measuring how far from the edge of the gear housing is the actual lube passage that oils the rear pinion bearing. Since the 18708 seal was about 1/4" shallower I'm thinking maybe the lube was directly spraying up right at the seal and overpowering it somehow?

For now I'm going to cross my fingers that it stays nice and dry LOL!

Speaking of bolting it all together...can anyone tell me what torque is required for the U-bolt style yoke 'straps'? The billet yoke I have uses the U-bolt instead of a strap retainer...not idea how tight to get them though.