I also had a fluid exhange/flush done by a BG shop (15+ years ago) on my 96 model, took 16 quarts IIRC. Only concern I had then (and now) is how often anyone cleans out the tank before they pour in the new fluid or change the filter on the machine??
Now I'd just do it myself as mentioned above.
What model 80 series/transmission?
Either way, they all use the same ATF, Dexron II/III compatible fluid.
Been discussed before but it takes around nine drain and fills to change
out most of the old ATF, so easier and cheaper to just do a complete fluid exchange.
If you do just a drain and...