i worked at a oil change place for three years and we did those kind of transmission flushes and it does replace all of the fluid. If the person had never had there tranny fluid changed and it was over 100,000 miles they had to sign a waiver saying we were not liable for it to stop working. when my tranny started to slip really bad i changed the fluid, filter and added some lucas and it is still going strong with 181000 on it, and i did the change at 124000

 

my old 87 3.9 wasnt vacuum advanced either, it was just centrifugal advanced.