It is a rough method, but...
Get a nut of the same thread size that is on the shaft (if the shaft is what came with the kit, that would be M4).
You will need some sturdy tubing, slightly larger ID than the shaft, but not so large that it will go over the sterntube.
Cut several pieces of that tubing, slightly shorter than the protruding part of the shaft, such that you can slip the piece of tubing over that end stump, and still place the nut with good purchase on the threads. 3 or 4 pieces should be enough.
Lubricate that tubing, the nut and the thread with some grease to prevent marring or fretting, and tighten the nut. That will pull the shaft backwards and it should not take too much effort breaking the shaft free by tightening the nut.
Add another piece of tubing if you reach the end of the thread, and the shaft is not free yet.
It is NOT sufficient to only make the shaft movable: there will be dirt, debris, corrosion and other crap in that tube, running it "as is" will very rapidly cause problems due to wear.
What is holding your shadt right now, is most likely corrosion between shaft and endbearings. These endbearings are only somewhere between 1/2 and 1" in length, so near 100% sure, once the shaft has been pulled more than that, at least it sould come loose.
Worst case you have to continue adding these pieces of tubing until the shaft is out all the way.
Once out, you can polish the shaft, carefully ream the bearings with a 4 mm drill bit, flush out the tube (WD40, brake cleaner, something like that, it is going to be messy :( ) and reassemble.
Removal of the tube from the hull will be a chore, but IF you manage, my advise is to buy a Raboesch mainenance free shaftset.
Those are BRILLIANT, 100% watertight and they are as advertised, absolutely maintenance free. A bi pricey, but these shafts will outlast you...
