2 jaw pittman arm puller works great.. though i have done them with them jinky small 3 arm gear pullers.
the 2 jaw pullers are wide thin jaws with liks and they are bolt retained to the puller body so they have limited movement and grip the sector arm good.
a couple whacks with 2 hammers.. using 1 as a backup, hitting 180 apart will swage the joint and let that arm slip off the splined shaft easier.
a lil penetrant oil never hurts either.
if it continues to fight.. you CAN use heat.. though you will be for sure rebuilding the box if you do so.
I've never had to use heat on one to get it off.