There is an alternate way of getting it apart and putting it back together. Clamp the shift lever in a vice with protective jaws and face the bottom of the tower up. Remove the rails and forks. Clamp a pair of vice grips tightly around the ball end of the shifter. With a large screwdriver pry the spring retainer out. This will allow the spring to move up against the vice grips. Place the tower facing down on a work bench and remove the vice grips while holding the tower down against the bench.
After addressing the repair of the ball on the shifter, and the worn area of the forks, place the spring in a vice and close the jaws with a small portion of the spring protruding above the jaws. Slip a length of safety wire through spring and twist it tight. Rotate the spring and add two more safety wire raps evenly spaced. Put the collapsed spring in the tower, add the keeper and cut the safety wire. Fish all the safety wire pieces out.
This is not the recommended way to go about the task. Buy the tool! But it can be done this way, just be careful, the spring is not lethal, but if it thumps you in the head it will hurt.
Tom Endy