This isn't on a Mercedes Vehicle but wanted to share it with as many people as possible.

One of my vehicles is a 98 Dodge Grand Caravan. For a couple of months the key was not turning in the ignition. A couple of weeks ago, I didn't think I was going to get it started again without having it towed. I searched the web for a possilbe fix and many others had similar problems on the same type vehicle. The temporary fix was to hit/tap the key with a rubber mallet while in the ignition. It worked but too unreliable to continue to operate this way.
Anyway, I called the dealer, they wanted $91.00 for a new ignition tumbler. Another $42.00 to recode it (match it to my existing keys) and $150.00 to install it. The parts guy happened to say the locksmith (larry's in Cinti.) can re code it but he didn't know how much it would cost. I called Larry's and he tells me yes, I can recode it for $20.00. So i'm thinking, cool I already saved myself $22.00. I continue to talk with him and it was brought up that he has them in stock, I ask how much and he says $37.00. I thinking, great I just saved another $50.00+. He then tells me it would be $37.00 for the tumbler and to recode it. So I call a local guy and ask him if he could put it in and what he would charge. He says $50.00. At this point I'm having a great day. I went from $300.00 to ~$90.00. So I went to the locksmith and picked up the tumbler. He is rekeying it for me and I say to him jokingly, All you have to do now is start installing them. He says, we do that. I say how much, he says $60.00 for everything. He had it installed in about 10 minutes. I went from $300.00 to $60.00.
Hopefully this will help someone. I don't think it is vehicle specific to get it fixed like I did.
Mike

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1999 E300 Turbodiesel
179,000 Miles