Mine was not that hard to do, but I did all of what you had done (less the gear puller), along with putting the nut back on (more surface area) and holding a good chunk of wood against it while wailing on the wood with a hammer. I think heating the cast arm was the most helpful thing, but if you wait too long after heating the heat will just migrate to the ball joint and it will not help.
If all else fails, leave it for an evening and try again tomorrow. That works for me more often than I care to admit.
Mark
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