It looked like the end of a shaft to me too but Dave, I hear the ring of conviction in your statement so I am convinced. I'll try to find a wee freezed plug for that thing. Not sure how to remove that old plug. Maybe drill a hole in it, stick a slide body hammer in the screw hole and try to pop it out that way? It works great and nothing else seems to be leaking so I'd hate to remove the unit. You know, if it ain't broke, why bend a wrench? How about if I just put some Bubble Yum bubble gum on it and call it a day?