Steve...........I'm pretty sure the seal is leaking because the transmission oil keeps decreasing and the level in the differential keeps increasing.
But why do I have to remove the pinion ? Doesn't the drive shaft come out with the pinion attached ?

I like the idea that oil may be leaking around the OD of the oakie, but I don't think it would leak as much as I'm experiencing. I'm adding about a pint of transmission oil every 600 miles.