Remove the Tool Release Piston from the machine. Now you can remove the Bolt from the aluminium base. Have a look to the left hand screw on the bottom side and check the other snap rings.
The drawbar is inside the spindle, so you can't see the position with the TR Piston on the machine. If you have remove the TRP check the retaining ring wich clamp the drawbar in the correctly position.
I think on this way you can localize where your problems come out.
With the TRP standing on a normaly table it's also a lot easier to push the spring and the round plate back on the bolt to install the snap ring.