Dr. Diff has you covered.
Mopar 8 3/4" (8.75) Pinion Seal for 742 or 741/489 Case
I will add my pinion leaked on my 742 case and it was the sealing surface on the yoke that had worn to where it no longer sealed. I replaced the yoke and the leak was gone. So you might inspect yours.
There are several other ways to fix that, they make sleeves to go over the worn area and they make seals that are shifted to seal on a different area.
8 3/4" or Dana 60 Pinion Yoke Repair Sleeve