I encounter this problem a few times a month. There are several little tricks that will get the key to turn that one last time so as to get the tumbler out
1.) get some dry graphite spray, spray just a little on the key and re-insert it into the tumbler. jiggle it a little, you may get lucky
2.) If graphite spray doesnt work. Get something that vibrates. I use an engraving tool. Put your "vibrator"
on the key while its inside the lock cylinder. Sometimes this will free up the stuck tummbler
3.) If none of this works... well your in for some fun. Gotta drop the under dash panel. get some masking tape and layer it up on the vinal around the steel retaining collar. Get a drimel with a cutting disc and cut off the outside lip of the collar. This will take some time and some cutting discs.
Now if you dont have the cylinder removal tool, get two paper clips and straghten them out. There are two grooves down the side of the tumbler. Slide your paper clips down those grooves to release the retaing clips to the collar. You will now be able to slide the collar off and the tumbler will come right out.
You will need to get a new retaining collar along with your tumbler set
Reinstalation goes as follows. With a flat head screw driver, turn the ignition switch to position 2. one click. With the collar, key and tumbler assembled line up the grooves on the side of the lock cylinder with the two grooves on the face of the cylinder. Use your paper clips to pushl back the retaining clips. The paper clips will serve as a guide on those two groove. Slide the whole thing in and remove your paper clips. This will lock the collar into place.
Whenever your ignition lock cylinder starts to catch just a little bit, replace it immediatley. Its much less difficult to change those SOBs when the key will turn