There's a DIY article on replacing the ignition tumbler (after the key won't turn) on a W201 chassis. It might not be exactly the same as with the W124, but, it'll definitely be similar.

Here's the link: http://www.peachparts.com/Wikka/W201IgnitionSwitch

I just did my ignition tumbler. It started to hint at the tumbler not turning...and that was enough for me to change it. Much, much less work.

Good luck

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
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