Very good. There is a set screw type thing, four sides easy to grab with a crescent wrench, at about 4:00 or 5:00 just like you said. It started to come out real easy, shiny threads and all. I stopped from unscrewing it all the way because it felt like there might be oil in it already. There is an identical set screw at 12:00 that came out just as easy. I'm guessing this is the fill hole. Thank you for the information.