For those in the camp of "if it ain't broke, don't change the fluid" voicing an opinion that new fluid with fresh "chemistry", like detergents and suspension agents, will stir up the debris that has collected in the nooks and cranys of high milage transmissions and valve bodies?
Certainly there can be no argument that the enhanced lubrication properties of fresh fluid will be good for all the mechanical functions of the transmission. Plus, clean fluid "should" flow better than the fluid that is burdened with sludge. Some would say the "Hunt and Thump" symptoms are due to low flow rates. I have seen no references that would suggest that fresh fluid would be detrimental to rubber parts like piston or shaft seals etc.

Perhaps a useful yet conservative approach would be to change the filter regularly, and only exchange that fluid lost in the service with fresh.

My own experience with 100K miles plus transmissions,(A8, A6 and a GM 4l30e transmission) is that fluid and/or filter changes cause no problems.

Dissassembly of a high milage 5HP24a transmission Valve Body (VB)shows lots of accumulated grey sludge, but no sign of anything collecting on the several screens and filters within the VB. Also, all restrictors show nice round holes with now buildup.

Information is good.

Regards

CalG