The automotive belt market is dominated by Continental, Gates, Dayco, Bando, and to a lesser degree Mitsuboshi. The Mercedes OE belt for a 2010 E550 is made by Gates in Spain. There's nothing special about the OE belt, so any quality Bando, Gates, etc belt will do. The aftermarket Gates K060945 belt that you can get Rockauto is not the exact same as it's a few mm longer which is perfectly fine since that slack will be taken up by the auto tensioner.
