I just had a tumbler go bad, and it was brand new. Got to use it twice, then the key wouldn't turn. Spent an hour trying to work it open to no avail.

I removed the whole ignition and then drilled down on the spot that gets depressed, when you can push the release tab down. The lock cylinder popped right out after that with a tap on a chisel. All it has to do is clear the rim around the housing. I wish I knew how to post pics here. It was very easy.

It was actually harder to shove 2 different screwdrivers into the bottom of the ignition cylinder void, and get the spring loaded tab depressed while turning the ignition switch to the position it needs to be in to insert the new lock tumbler.