I JUST finished going through this today with my car. The cooling lines to my tranny have apparently been plugged for a long time now (no flow) and the thing has been slowly cooking itself. To make a long story short, I got a new tranny and had the external cooler installed. I did this because I experienced the value of one when my dad installed one on his 85 Chrysler 5th avenue. He used to drive around all day in desert-like conditions in a 4000lb non-aerodynamic car, and the tranny did well. So, for the $140 clams or whatever that is U.S. $, I said "DO IT" and had it done. A cooler is far less expensive than a new tranny, heh, and they work from what I have seen.