Whilst on the Lexus GS Wiki page, I found out the transmission is an A960E for 6-speed, and AA80E for the 8-speed.
As a result of a bit of searching, these came up and thought they may be of interest and use to the members:

http://www.trnw.net/z-search/A960E.php
http://www.trnw.net/
http://www.trnw.net/shop_locator.php

http://www.raybestospowertrain.com/r.../RCP96-206.pdf

https://www.automaticchoice.com/Catalogue/aw_a960e.pdf

And something that's piqued my interest.....

http://www.lubegard.com/pdfs/Lubegard&SwissMotor.pdf
http://www.lubegard.com/pdfs/ATFComparisonbrochure.pdf


Hopefully some of that is useful.

 

Thanks Boron. I believe the transmission maintance on these cars is very important. The very first thing I did when i got my GS was flushed 11.5 quarts using Amsoil equivalent that exceeds Toyota WS

 

Lubegard is excellent stuff I used it before on an Acura when I had a ticking noise comming from the trans .
After one bottle the noise was gone.