EPCnet Online is the official Mercedes-Benz USA site for obtaining replacement parts information for Mercedes-Benz cars and light trucks.
EPCnet Online is a browser-based Electronic Parts Catalog which allows the user to specify virtually every spare part for the models covered. An intuitive graphical user interface permits easy navigation though the extensive parts catalog. Brief tutorials are available at no charge to familiarize new and experienced users with the Mercedes-Benz spare parts group system and the selection of the appropriate part for your particular vehicle
You can subscribe to EPCnet Online for free which covers North American cars. Go to the following website to subscribe: https://epc.startekinfo.com/epc You will need a valid Visa/ Mastercard/Discover or American Express card to subscribe, but it won't be charged unless you wish to have access to the worldwide MB part numbers, which is $12 for 12 months. Note: I'm using Windows7 with IE8 and EPCnet worked fine for me.
I was able to print exploded part diagrams with the part numbers for my 2003 CLK320. With the knowledge of the proper part number, this made ordering parts a snap either online or at the local dealer.