i'm scheduled to bring my GS4 for a tranny flush... should i just go for a fluid change or should
i drop the pan? i was quoted $120 to drop the pan..... does the GS4 have a tranny filter? will dropping
the pan change all the fluids in the tranny?

 

The factory manual advises to drain and refill the transmission oil pan which should only take 2-3 quarts of Type T-IV fluid. Do this service every 15-30K miles for optimum transmission life. When the transmission has about 150,000 miles or more then it would be advisable to drop the pan, clean the magnets (here's a really dirty magnet: http://www.saber.net/~monarch/magnet.jpg) in the pan and clean the transmission filter screen.

Using the correct fluid (genuine Toyota Type T-IV) http://www.saber.net/~monarch/typet.jpg instead of imitation products (e.g. Amsoil "Universal" & Valvoline "Universal") and meticulously maintaining the correct fluid level are the important factors in long transmission life.

Unfortunately many shops, including Lexus dealer are sometimes sloppy about getting the fluid level correct and sometimes use imitation fluids which may not be as good for the transmission. Then they turn around and try to sell you a "complete transmission flush" for $100+ dollars claiming it will extend transmission life alot better than simply draining and refilling the pan. No Toyota / Lexus service or technical training manuals advise doing a "complete transmission flush" and there are risks involved with the procedure which I personally would rather avoid.

 

I would just drop the pan, clean the screen, and use either the OEM Toyota FIPG or a aftermarket gasket to seal the pan, and do a incremental change. I do not like the fluid exchange method, because 99% of the time, they will try to sell you a harsh flush, heck even the dealer uses a flush made by BG or MOC that can be rough on the tranny.

 

There is DIY on bananags's website.
Thre are some Dealers and maintenance shop chains that do run arounds on you if they think you don't have clue about about cars to get some profit.
There is a saying, "If you want it done right, do it yourself"