Absolutely not. By law, you may have your vehicle serviced at the facility of your choice. As long as the services are performed properly, the manufacturer cannot void your warranty. This is one of the reasons it's important to maintain a history file (note: we save all service history electronically). The only time you are "required" to return to the dealer is for factory warranty repairs and recalls. Even then, you may have those repairs done at any repair facility, but the vehicle manufacturer will not cover the cost.
If you have your vehicle serviced at Stuttgart while under warranty, we will make you aware of any needed warranty work so that you may return to the dealer and have the repair covered at no charge to you.