You might want to price a replacement shaft and coupling to see how that stacks up against labor time and options for unsticking it. Bearing in mind that you are working in a confined space...sometimes a dedicated penetrant like Kroil or PBlaster will drop things apart. They attack the chemical bonds, they're not just lubricants like WD40.
And when all else fails, a slurry of dry ice in alcohol, or a CO2 extinguisher, can be used to freeze-cycle parts and make them come apart without the risks of a torch. Used judicisouly, a torch has purposes too. But there are alternatives to just whapping it with a hammer, and sometimes penetrant and a properly improvised shaft puller is all it will need. Sometimes, it is easier to take a Sawzall and simply be done with it.