Take hella's advice.
Try it with the small key several times. Try inserting the key with the board horizontal, diagonal, vertical, etc, to make the spring flop in different directions as the sleeve slides over it.
Take off a few keys and look at how the springs flop in other holes, and how they are centered on their bases. If the bad one is off-centered or otherwise cock-eyed at the base, or does not move around like the others as you tilt the board, you may have no choice but to take it apart.
A bolt-mod is a great idea, but save it for last if you are timid.
Last, you never said whether the spacebar actually works, I assume it does not. If it works, live with it, and save the project for another day.