I am linking to this thread as a decent explanation of what to do
when the key-does-not-turn-problem is not the tumbler.

http://www.peachparts.com/shopforum/showthread.php?p=355575

Tomorrow I will add some pictures from my own steering lock that stopped
my key from turning problem.

At this late hour I have finally disassembled the ignition steering lock
and am ready for the reassemble with nothing more than ignition switch
and key and tumbler.

I got stuck at the gas station and the car would not start.
At first I blamed my new tumbler and key.
After getting that tumbler and key to finally turn, and getting it out,
the mechanism behind it would not turn with a screwdriver.
My conclusion was that the ignition and steering lock were somehow the problem.

I got it out, I got it apart. Tomorrow I will add my picture of what it looks
like.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250