We haven't sold cup grease in over 60 years. And it was a soap based grease that wasn't very good. Modern trucks have a filler plug. Before the factory installed fill plugs, we drilled a hole either in the axle flange or in the hub between the two bearings and threaded it 1/8 NPT. We then squirted 80W140 in the cavity and installed a 1/8 pipe plug. This avoids the risk of packing the bearings with a grease that is not compatible with the lubricant in the rear end. Back when the book was written hypoid gear was compatible with cup grease. I use 80W140 in my fleet of trucks as well as my antiques.