Best guess is there is a build up of old grease or other "Lube" in the cyl or the mechanisms that wont let it return on its own. I assume there is a return spring in the mechanism somewhere and that might be the problem?
If you were to remove the battery and turn the key to the start position would it eventually return to run? maybe with a little tapping on the column near the key. That would show that the return spring is good and it is just gummed up.
