I'm buying my first MB, a 2019 GLC 300, later this month. It's currently a dealer loaner and after it comes out of the loaner pool, we are having it certified. I'm interested in purchasing a 4 year prepaid maintenance plan but have been told that a pre-owned certified can only go up to a 3 year plan. It should have 3-4 k miles on it at purchase time. Does anyone know if that is accurate?