Yes, you are correct. Consistent with others, better to not let them monkey around but to consult Germany. My dealer told me that there were only a couple of trained techs for our car. Translation, we don't know.
Be sure to read up on this topic and press to talk to the actual tech vs. service advisor unless he/she has been with you for many years. Don't know if yours is a lease or purchase but if the latter, wouldn't it be great if they replaced the motor under warranty?
Jeff in NYC
MB '17 B250e; MB '06 E500W; MB '81 380SL