That's 2-year-old for broken.
All real W124 owners have replaced their ignition switches at some point. I don't recall if the symptom was a key that won't turn, though.
We have also all replaced the neutral safety switches. I think the key turns, though.
The one thing I know that prevents the key from turning is the wondrously designed, high-tech shift interlock. This is a cable from the shifter to the steering column that is adjusted at the side of the shifter. It's one of the finest bowden cable designs ever made. It probably had its roots in the 40's or 50's but made it into the 90's on the 124. When I saw it on mine, I knew it was time to move on to the electronic age.