Key won't turn in 190E ignition

I just sold my 1989 190E 2.6 to someone who now finds he can't turn the key in the ignition AT ALL. I checked to make sure he had jiggled the steering wheel, and he had. There are two alarms in the car, the factory installed one, and another one with a remote. I someone have a recollection of a problem with an ignition lock relating to one of the alarms, but he has locked the car and turned off the secondary alarm with the remote, and opened the car with the key, and no alarm has gone off at all. He feels the ignition may just be shot at this point. Could there be some other answer here? It worked fine all the years I owned it.

replace that ignition switch

These cars are known for having a failure with the ignition switch. Just replace it. Thats what I did.