Your ignition switch may be operating normally. For several years, Chevrolet, and others, I think, had a lock position on the ignition switch that locked the switch when you removed the key. The normal Off position allowed removing the key, but also allowed turning the switch on without inserting the key. That was thought to be a convenience at the time.
As for repairing your lock cylinder, probably it can be repaired, but you have to get it out of the switch housing. It sounds like you are going in the right direction to remove it. When you depress the spring as you said you can, turn the cylinder to the left- then it should slide out. Then take the cylinder and key to a lock shop or hardware store that can re-key locks. They can replace the tumblers and springs, and probably keep the same key code- same key.
Harvester
