I purchased this differential cover a while back - had the shop put it on during gear install. http://www.americanmuscle.com/frpp-88-diff-cover.html Now I'm in the process of changing the gear oil. Got everything drained out, but I cannot figure out how to remove the fill plug in this cover. It is some large sized hex. A T-50 torque bit is too small and a T-55 is too big. Does anyone know what is supposed to fit in there, nothing I have around the house seems to fit? I already tried to remove the factory fill plug, but ****ing blo-hio has the thing so rusted, it is not coming out .