I've never really paid attention to the door closer thing much. But the door is slamming when it closes. I notice there is a screw plug on the door closer. I took the whole door closer thing out and drained out the fluid, it came out like brown paint. I had some floor jack oil so I filled it up and drained it a few times. I hope thats the right fluid to use. Even after I changed the fluid, it still slams the door. So is there a better fluid to use?