If this is a full floater hub type rearend, you don't pack the bearings with grease. When they have been all apart and completely cleaned of grease, you would need to put a little grease on them until the rearend fluid works it's way in.
There is a seal inside the hub. It rides on the support tube. You will need new metal gaskets to install between the axle end and the hub. I would suggest using RTV on the rear cover. If this rearend is of the hypoid design then the fluid should be hypoid high pressure lubricant.
