The ring an pinion are not dependant on fluid to turn each other. If the drive shaft is spinning and you are not moving, you have big issues. Remove the bolts and take the cover off. RTV is normally used and not a gasket.
2003 TJ, 33" BFG AT, 2" BL, 2" BDS spring lift, Truck Lite headlights, Homemade sunrider top.