Hi all, I bought this RS gas cap and it came in a GM box with correct part number 3910189. I bought it on the premise that is was GM NOS but I did not pay ebay price for it. I notice that one just like mine sold for over $180 recently. I also notice that some have screws on the back and some have rivets. Please tell me if mine is an original. I do not see a part number on it anywhere.