Ignition switch problem...

I have a '72 Mach 1 with a 351 Cleveland and a toploader - fairly stock stuff. My problem - today - is the ignition switch. It turn clockwise just fine, but it will not turn Counterclockwise at all. For years it worked well, then the counter clockwise movement started being hit and miss. Now, it simply will not go to the accessery side at all. Has anyone run into this?? I am open to any suggestions before I tear into that column.

Lockset cylinder...

Thanks for your note - I want to be sure I understand.
You replaced the entire cylinder in the column. Pull one out, slip in a replacement cylinder ( which had obviously new keys with it ) and all was well??