Don't know who at MB decided that the fluid isn't supposed to be changed, but that is a farce! After replacing & repairing 100+ of these transmissions at dealer(retail center), I would suggest service before the 4yr/50k mi warranty expires. & then service every 50-75k miles.
MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 16V ITS SCCA racecar