I have the same problem. Haven't had the time to fix it, but I know what the problem is.

Part 7, the starting switch, worked itself loose. With that part loose, there was play at the back of part 5, the locking cylinder, which caused the tang on the back of the cylinder to break off.

With luck, your switch is loose and tightening will fix it. If you are unlucky, the cylinder will have to be replaced using the paperclip method.

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1983 300SD "Guderian"
1987 MR2
2015 Camry
2015 Chevy Spark
2006 Hyundai Tucson