It varies by dealership, I believe. I think that ALL 2008 smart dealerships are probably prevented by Penske from openly working on 450's or buying parts for the 450's. If you have another Mercedes dealership in town, check with them. The service departments are supposed to be independent profit centers from the sales departments. That would usually give them some matter of choice in whether they worked on your car (and supplied parts) or not. If you can't get parts, but have a dealer (any shop, Mercedes or not), let me know and I'll get you, or them, the parts.
Ron Gaus, asmartcar.com