Per the transmission....With 56K, get it purged. Reason? Because if the car turns out to be the steel and iron brick that it is, you may end up keeping it another 50K. If that happens then you are going to have to decide at 100K, if you should have the fluid purged. And you are going to have to listen to this point/counterpoint again. Except the stakes will be higher because the tranny is older.
I don't know why there isn't some hard statistics on this subject. The anecdotal has raged on this for as long as I can remember. The concept that a mechanical device develops some kind of organic, symbiotic environment has always confounded me. And this is how bad it has gotten....
Five years ago, a local Jiffy Lube started doing purges. My wife'* Series I had 100K on it. To have it done, I had to sign a waiver stating that my car had over 100K and Jiffy Lube could not be held responsible if the trans failed?!?! I know why they did it. Because more trans fail after a 100K, and somebody in the legal department wanted to cover JL'* butt. But that kind of thing just reinforces the "don't touch it" theory.
My theory for the average driver.... get it done every 25K. Then there is no possiblity that you will ever have to depend on some little elves created by your 100k mile aged transmission fluid to hold it together.
Then, If the transmission fails, you know it is a result of an engineering/manufacturing mechanical issue.... you can blame the car manufacturer and stick it to them by not buying their cars again
1995 SE ..Green and Rattle Can...234K mi...Bonnie (she'll outlive me)
1998 SSEI .. White ..119K mi...Evey
1996 SSE ..MajTeal..157K mi...4/12- Dealer trade full of Lucas Trans fix