You might try running the VIN at a Stealership and find out what (if any) records there are as to transmission work done on your car.
There are diagrams in the locker regarding adding an external/additional cooler.
Cleaning and flushing the system, adding/replacing the filter (seems strange that a '92 wouldn't already have had the external filter kit done under warranty?) and fluid certainly can't hurt.
Your tranny may last for 100,000+ miles.
