Every month? Why?

MB intended that the fluid never be changed, which is why the dipstick has that "lock" on it. While, I would not say that "no change" is not the best plan, and certianly after 110K a change is probably in order, there is no reason to ever change ATF in a car more often than once a year at the most (even in hilly terrain or with a trailer involved). The only reasons to change ATF are to keep it from sludging (which modern ATF really takes a long time to do) or to get rid of fluid contaminated with metal particles from wear on the gears/clutches/bands. If any car is wearing things so fast that changing the ATF every month results in noticable metal, then something is definetly wrong (and I doubt even possible as the Trans. would have died a long time ago).

I have to ask, if you change the ATF every month, how often are you changing the oil?