Jerky, poppy steering (74 Duster, 318, 904, auto, column shift, power steering car)

Well, we should be able to rule out the column, if it was doing it before. What about the gear box itself? Don't these have an adjustment to take up play between the sector shaft and worm gear? Perhaps the gearbox (or the pump)is plain worn out. I'm assuming you have checked other steering and suspension components for wear, and regarding the pump - there is fluid , belt is tight, etc.