I have a 2006 Monte Carlo i bought used. It's the basic model. Its my first car
​​​​​Basically, the car runs perfect except when I try to shut it off, occasionally the key wouldnt turn all the way off and I'd have to put in a small amount of force to turn it off. It beeped at me and left my lights on like my key was still in the ignition. I was able to fix it by starting and stopping it a few times, and eventually basically got rid of the problem by spraying some WD-40 on the key as I saw advised on some car forums.

But a few months later the problem has returned and WD-40 isn't doing anything now. Turning it off and on, wiggling it in every direction, no matter what I do, it won't release the key without force. I was forced to let it sit for the night and that killed the battery, which now won't jump (getting it tested tomorrow).

What do I do? I had guessed replace the ignition cylinder lock thing Incase the tumblers were bad, but i can't guess wrong with this. I'm extremely poor and can barely afford even that repair. Someone please let me know if that's the issue, or if it sounds like something else. I know nothing about cars and I'm totally lost.

Also, if it is the cylinder, where do I get that? Can I replace it myself?