Sorry to hear of your difficulties removing the outhaul shaft. Also interesting to see the different mounting methods used by Amel over the various SN boats. I don't have any specific answers to getting the shaft out unless it would be to use dry ice to cool the shaft and/or applying heat to the gearbox shaft. Like so many things this is an all hands on deck situation so penetrating oil, heat, cold, vibration, and pressure may all be needed.
Note that there is no seal between the outhaul shaft (male) and the gearbox shaft (female) into which the outhaul shaft inserts. The only seal here is the lip seal that is press fit into the upper cover (and lower cover) of the gearbox and provides a seal to the gearbox (female) shaft. I have found that removing the outhaul shaft once yearly and lubing it has always yielded easy removal, not sure why your's is stuck after so little calendar time. I do rinse thoroughly the areas of the outhaul and furling gearboxes with fresh water after every sail and I do slather an unsightly amount of grease around the upper surface of the shaft/shaft interface but it sound like you do the same. Eric suggestion to remove a couple of thousandths from the keyway seams reasonable, perhaps an easier thing would be to remove a couple of thousandths of an inch from the shaft itself (larger bearing area and hence a larger "sticking" area).
Wish you luck,
Gary S. Silver
Amel SM 2000 #335
Puerto Del Rey - Puerto Rico