[macojoe]

How long has the boat been sitting?? If it has been years then yes go for the whole new tube, but if its just been the winter then you might be able to save it.
Cut the end so there is nothing to hold it in. Then trying driving it back in and then back out to get it to free up, spraying after each attempt.
You can also drill a small hole in the tube in the middle and try spraying some PB Blaster or Kirol in there and let it sit for a bit.

If this doesn't work then you will have to replace the tube. The tube is not threaded all the way, just remove the nuts on each end and you can drive it out while pushing the new tube in with out removing the motor if you are lucky!

But if it is that bad you might be better removing the motor to get a good wack at it, and you will not be the first to have to cut it in a few pieces to get it out!