change tranny fluid on a 97 e420?

[dirtysocks]

I did a search already but could not find much info on this topic. My dad has a 97 e420 that is "due" for a tranny fluid change. At least that's what one source says. There are conflicting opinions on this subject. He read one place that the fluid should be changed every 60k miles, and somewhere else said that the tranny system is "self-sufficient" and the fluid never needs to be replaced. I did not believe this "self sufficient" stuff at first, but after he told me that you actually have to purposely break a part and replace it just to change the fluid, I'm not so sure. Anybody know what the truth is on this subject?

p.s. He already bought the oem fluid and replacement for the part that needs to be broken.