If you can't easily turn the switch with the tumbler out, then the tumbler certainly isn't what is jamming it. Of course, insure your steering lock isn't tight against the switch (all cars). You have to file or pry out the stakes in the die-cast aluminum (?) body so you can remove the steel plate. If you spring detent has broken, it will just shake out.

You can then remove the steering lock rock if you desire. Those probably don't help much in anti-theft since it took just a few weeks for criminals to learn how to defeat them. Plus, no loser would steal an old M-B diesel unless they believe the prices asked on craigslist.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans