Well, it's cracked. How bad is it?

Yes, the outside. How far up to the outside of the hole does the crack come? I agree 100% thet you NEED to break that piece OFF and file the edges down. That in itself will stop the crack because the piece will break off AT the crack's end. Once broken off and filed, the crack will be fixed. As long as there is still enough length to the hole and the tube will still press in, it will be fine. Besides, doesn't the tube have a bracket on it that attaches to the head? If not, PUT one on it.
Another vote for breaking the piece off.

The outside doesn't appear to be cracked at all. The crack seems to be completely on the underside. I just worry how much will pull off with that piece if I grab on to it and try to break it off. But, like you said, no more crack. There should be plenty of length left to the hole as the tube does not push in very far at all from the top. There is a bracket on the head to attach the tube. So the hole on the underneath side I assume is just to help guide the stick where it needs to go? As long as it still routes past the windage tray I would be ok there.