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

You need to get the rest of that tube out so you can see how far up that crack comes.
Agree with this and with Greg. That tube has to come out. While I think I can see the end of the crack and it seems to be only on the underside I won't know for sure until the tube is out. Not to mention it has to happen before the new tube can be installed.

From the ideas I haven't tried yet pile I will try the pushrod from the bottom and maybe the dremel to remove the "chuck" which I'm still not clear on. That hole is pretty smooth but I still think I see what could be the end of the tube about halfway down that hole. It seems tube removal should come first before a final decision about the crack can be made.