8 3/4 Rear End - General Questions, Seek all and any help, 1st restore!

If you replace the pinion seal you will be removing the nut off the pinion and taking the yolk off. Inside behind that bearing is a crush sleeve. If you take and loosen that nut you will probably be needing a new crush sleeve which means completely disassembling the differential to replace it. Therefore if that seal doesn't leak I wouldn't mess with it. Also was the rear end making noise. If it was then it could be bearings or it could be teeth on the gears or it could be several different things causing that. Personally if it's not broke don't fix it. 
Hang it up and spray it out with some PB Blaster. I'll let it drain then shoot some oil in there to lube everything up, bag it and tag it until you're ready to use it.
Jmho