Help with my wheel hub please

I occasionally pop the rubber cap off of the hub cap and check the grease. I haven't repacked a bearing since my 1971 Mercury Comet GT days. I did replace one of the hub caps with rubber cap that looks like what yours is missing. Mine had a ding in it that had me concerned about the cap sealing. Pry the old one off with a screw driver and drive the new one on with a block of wood and a short sledge hammer. They can be ornery. I think it was around $8. That stinks that a shop did you that way. Should be an easy fix though.