So I climb under my TJ this morning to change the diff fluid because I notice it's been leaking and it's about time for a change. So I go to remove the filler plug and instead of a metal threaded plug, there's this piece of rubber similar to the drain plugs in the body, with the Dana insignia molded into it...and surprise, surprise, that's what seems to be leaking. Shouldn't this plug be a steel threaded plug??? I'm a bit confused and don't want to mess with it so I don't make the leak worse. any help would be appreciated.