8 3/4 grease leak .

I disagree, many of the diffs i have had apart have sealant on the splines,a rubber waser/insert
Or a rubber coated washer that seals spline. Service manual will specify the method of sealing.
MY mistake, I was thinking the sealing surface was on the pinion shaft, forgot it was on the yoke.

slapping forehead!

I deleted my post to not spread false info more than I did!