I'm not sure if your car is like mine, but in order to replace the ignition tumbler, you're going to need to get it out. Unless you can turn the key to the second position to insert the tool in the holes, you're going to have great difficulty removing the ignition tumbler. Maybe it would make sense to try to get the broken key out and just order a new one from your local dealer in the mean time.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles