I would strongly recommend replacing it with a new one - it is the "tee" shaped thing and is called a steering lock. I have a used one from a 300D that I am willing to sell cheap BUT you will not be in much better shape than you are now. The steering lock cost around $175 (I think). In my 300D I replaced it and the tumbler at the same time and should be good for another 200k miles. I just replaced the tumbler in the 240D and will keep an eye on the lock because I could see some slight wear on the point where the key pushes on the latching mechanism. Easy diy'er job once you have done one.

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Jim