Welcome to JustAnswer, my name is XXXXX XXXXX X'm here to help get your problem resolved. Please feel free to ask follow up questions, it is part of the process, thanks.
I Think they sold you the wrong seal. But if you had a grinding hum, then you have a bad bearing and that slop is why the seal was leaking. In this case you are better off time and money wise to just get another rear end. Make sure you get one from a scrap yard with a warranty as you will know right away if there is something wrong with the new one and you can swap it out if needed.