when will my c-350 sport need transmission service. Mileage-40,000

Hello, The service indicator for you vehicle will let you know when service is due, and even which services are due. (e.g. "Service b due now") If you are wondering if it is time for the transmission, just look at your service interval indicator on the dash, see which service is coming due, and consult the owners manual for a list of services performed at that service interval. This is one reason I love Mercedes. Super convenient.