In the auto shop days we changed trans fluid on many of the used car lot cars. Most were already burned up and we could count on having plenty of trans work. On our regular customers service a routine trans filter and fluid change was not a problem. I guess when the trans failed it was easy to look back and say 'well trans fluid was changed and 2 weeks later the trans failed so changing fluid was not a good idea."
today.. do I change my streetrod trans fluid....not on a bet. haha it's nice and red and has never been over 200 deg other than when it is 99 deg outside. I don't even like to change the oil if it is clean.