I'm sorry to hear about your experience at the MB dealer. I guess I'm fortunate. After I got my van I ordered metal valve stems all around. When to my local dealer, they have a separate Sprinter van servicing unit at the dealership. They changed out the valve stems, balanced all the wheels and the aligned the front-end. With the new valve stems I easily mounted my tire pressure sensors and everything has worked well ever since. It didn't cost that much, and what it did cost has paid dividends in tire wear, handling, safety, and convivence.
I am still OK with my existing (original) tires but will likely replace them with Michelin either after my fall trip or next spring after my winter trip depending on wear.