What i found was these hooks had over many years rounded off on the contact edges, and also were sloppy on the shafts on which they rotate.
Solution: remove lock and place flat in a vice with mechanism facing up. With a small flat metal file carefully file the contact surfaces flat again. To take the slop out of the shaft on which the hooks rotate you will need a hammer and punch. With the mechanism still in the vice place a scrap block of wood under the lock to take up the shock of what you are about to do. You will see the hooks being held on the shafts by some sort of metal flange sweated onto the shaft. Take the hammer and punch and work your way around this flange tapping it down and reducing the slop of the hook on the shaft.
This may make no sence unless you have the mechanism off the car and in front of you. A bit of bush mechanics but it has solved my sliding door problem for now. Good luck. Bill.