How often should the transmission oil be change in an E320?

according to MB, the Transmission Fluid lasts for a life time. However, I changed it at 100,000 miles, just for the peace of mind. I think it worths the investment (a $250 job). according to MB, the transmission fluid lasts for a life time. However, I changed it at 100,000 miles, just for the peace of mind. I think it worths the investment (a $250 job).