If the old shaft has been glued in then the best way to break it loose is to use heat. Ideally a small blowlamp would be best but dificult to use this without damaging the wood around the shaft. A soldering iron might do the job, put the end of the iron in the shaft tube from the outside of the hull and leave it for some time to heat up the shaft. Wiggle the shaft from the inside to see if it is loosening up, if it feels loose then use a wood block on the top of the shaft with a hammer and try and drift the shaft out while it is still hot.
Jim