2011 e350 a/c not working. I took it to dealer in 2018, they recharged the system. A/C worked until July 2020. Took car to dealer 8/17/20, advisor stated system needs recharge with dye. I questioned why is a closed system needing recharge -where is the leak? Advisor insists car was diagnosed and even install an A/C update . They do not see a leak.. Scratching my head, What's up here.