How to change ignition lock if key will not turn?
On ours 99 SLS we removed the housing around the steering wheel, to get access to the chuck and there is a pin in the far back of the chuck, my wife found it, she fiddled with it and the chuck and it came out. It took some womanly finessing.
How to change ignition lock if key will not turn?
A good locksmith might be willing to loan or rent you their professional lock removing tool.
Failing that see if AAA can offer assistance.