leak on front differential k3500

i have a friend with a 89 k3500 silverado with a 454 auto 4x4, ever since he first purchased the truck it appeared to be leaking oil from the passenger side tube where it bolts up to the center differential and i was wondering if there was any kind of gasket or seal that could be replaced to stop it from leaking

There's an axle tube that sticks out of the differential, ending in a flanged axle that the CV joint bolts up to...does it leak between the axle tube and the diff body? There's a gasket between the tube and diff.

Might as well replace the axle shaft seal also while your at it. Good luck!