Originally Posted by BillGrissom

Hope yours isn't like the issue in my 1984 300D. It felt like the tumbler was jamming, but when removed, it turned fine. At least you can get your key to the "can unscrew front nut" position where you can push in a thin screwdriver to push down the security tab. In mine, the culprit was a broken detent spring mount down deep in the cylinder stalk. I had to pry off the steel cover to find it. The spring mount is thin die-cast aluminum so easy to break over time. I just removed that spring, so I don't get as solid clicks, but the key has never rotated on its own while driving. Wish I had removed the steering lock rod while in-there, since not much theft prevention and only causes problems.