As of 2015, ordering a Mercedes-Benz replacement car key requires you to visit to an authorized dealership. It is the responsibility of the requester to prove ownership of the vehicle and the dealer to verify the validity of the request and to activate the new key.
When ordering a replacement key, you must verify your identity and proof of ownership. Bring an original state registration for the car along with a current driver's license, state identification card or passport to the dealer. Photocopies or duplicated documents are unacceptable, as are expired documents. If you're not the current owner, provide a signed and dated letter from the owner authorizing the request on their behalf.
After the dealer approves the request, he needs access to the car to synchronize the new key with the functions it performs on the vehicle. Some dealers offer this service at no additional cost, while others add a surcharge to the price of the key.
Mercedes-Benz provides an owner support center for questions at 800-367-6372. Representatives are available Monday through Friday from 8:30 a.m. to 10:00 p.m. EDT to answer questions. This number is active 24 hours per day seven days a week for remote door unlocks, and an automated system is also available for those who need to find a local dealer for key replacement requests.