Call Tim in Mercedes parts in the link below. Give him your vin number and he will be able to give you the correct part number. Sometimes it's a good idea to get a part like that at the dealer since if they give you the wrong part they will return it with no problems, so long as when you ordered it you also gave them your vin. Also the chances of getting the right part the first go round are improved, at least at Duval Motorcars.

http://www.trademotion.com/partlocator/index.cfm?siteid=213951&catalogid=0