i've got a 97 automatic with around 115,000 miles on it that i
bought used about 3 years ago i don't know the history of this car
the trans shifts perfect was wondering should i have it serviced or leave
it alone,i've been told if it ain't broke don't fix it, just trying to a avoid
a pay me now or pay me later thing! thanks

 

Having it serviced is not going to hurt it. I know what your saying though, but honestly having the fluid changed out with fresh stuff can only be a good thing at this point.
If something should happen, after a transmission flush than I would expect something else were wrong with it. Since you have had the car for 3 years, and it's been reliable, and the transmission shifts fine now, than go ahead and flush it, It will be fine.