I would guess they pulled the axle shaft out instead of pulling the lug nuts, is the wheel itself covered with oil? Is there oil on the back side of the drum or coming out of the drum? There will always be oil behind the axle flange, you can jack up one side at a time, so the oil runs towards the center of the truck and replace the gasket fairly easy. The oil will automatically filll the hub while driving, but adding some is advisable. If there is oil at the back of the drum, then your cost just went up, if the wheels are dry and it appears they shop pulled the wrong bolts, then you are out a simple gasket and a little sealer. As mentioned above, there is one hub seal at the back, and one gasket at the front, deterine which end is leaking and report back.
