Wow this thread certainly has gotten colorful. Time for me to interject my thoughts, opinions, and pictures on all this.
Having recently done a few drain and fills myself it would seem that i am uniquely able to comment on this particular endeavor.
First the pictures, which you can find here
http://www.mazdas247.com/forum/show...ATF-Drained-and-refilled-today-Lifetime-fluid
Of special note, the color of the fluid: not clear red, cloudy brown reminiscent of used motor oil, not ATF. I believe that would be considered "discolored" by the standards set forth in the manual for needing to be changed. Note the change in fluid color after just 1 drain and fill.
Next my thoughts and rationales for doing said drain and fill. Having a basic understanding of how these transmissions work. As it relates to fluid pressure actuating friction clutches, and small amounts of clutch material shearing off with every shift and thereby contaminating the fluid. It stands to reason that understadnding how this tranny functions then, that one would realize that the fluid would become contaminated after a time with the above mentioned friction material. And the tranny would be subject to this suspended material circulating around acting as liquid sand paper as well as becoming lodged at times in the myriad passage ways through which the fluid flows to actuate said clutches. Possibly at times occluding these passages.
The likelihood of the above happenning with contaminated fluid being much higher than with a fluid without as many suspended solids resulting from fluid being exchanged. I choose to drain and fill at regular intervals, because it makes rational sense... And the empirical evidence (pictures) provided above confirm the need for routine fluid exchanges.
Yes, i realize the manufacturer does not recommend routine fluid changes. But one must also realize that it is in the manufacturers' best interest to build a vehicle with the lowest possible cost of ownership in order to stay competitive.
While it is true that many manufacturers have designed "sealed for life" transmissions, one must also note that there are differing qualities of fluid put into these units. As someone had pointed out earlier they got 160k out of a Benz without any service. ZF, the company that manufactures trannies for Benz, uses a proprietary fully synthetic ATF that is far superior to the simple highly friction modified dinosaur juice placed into our trannies by Aisin. It has better shear resistance, and vastly better heat tolerance than the Aisin spec'd fluid, so we aren't exactly comparing apples to apples. Mind you, the ZF spec'd fluid runs about $20/qt at dealer cost.
The bulk fluid the dealers use to service your tranny is manufactured by Exxon Mobil and sold under their own brand Mobil JWS3309, Toyota T-IV, Mazda T-IV and also as Volvo OEM ATF, among many others. It's nothing special, and it's cheap. No way should you pay $10/qt for it just because it has a mazda sticker on the front.
As far as transmission specifics, there is a metal filter screen designed to catch large debris which become suspended. There is no need to replace it. Just clean and reuse if you desire. To access it you will have to remove the tranny pan and unbolt it from the valve body. You will also need to replace the tranny pan gasket with a new one if you are going to do this.