Do you usually need to replace the yoke too?
Based on that pic I'd say it was the tcase output that was leaking.
. Don't see any of that going on, just seems to be on the bottom of diff.Seems like if the pinion seal was leaking you would have gear
lube slung all over the diff.. Don't see any of that going on, just seems to be on the bottom of diff.
?and generally it wont drip upward onto the yoke... to be flung around.. just out the bottom of the seal...
check the fill plug on the side... and get a rear gasket and gear oil, and service it... it may just be wicking up from a cover leak.. pull cover, drain, clean, regasket, fill, joy..

Looks great! Someone will chime in shortly enough on your other questions. Why are you putting different wheels on it?