VERY familiar with that problem.
Our gearbox was actually past it's use by so we set to and cut through the gear to extract the shaft. It wouldn't come out even with a hydraulic press.
The shaft was badly pitted and clearly the steel/aluminium/saltwater combination had done its work.
The knob and the shaft are one piece alloy and available from Maud
No part #, just "Shaft for gearbox main furler" Eu139,00