203 589 02 31 00 Adapter kit - WS60.00-P-3015K
WARNING: This page is about a different car, the 2012 Mercedes-Benz C300, 2011 Mercedes-Benz C300, 2010 Mercedes-Benz C300, 2009 Mercedes-Benz C300, and 2008 Mercedes-Benz C300. However, it is still accessible from the selected car via links, so may be relevant.