Similar tread a few weeks ago.
I agree with **** above. Not sure why people want to confess to the dealers - next time you have that urge, think of how their sales people tried to sell you that last car.
If it fails take it in and let them look at it. Let them do whatever they want to the fluid. I don't believe the automakers and dealers are wasting their time with "tracers" - particulary T-IV since you can get the stuff directly from Mobil.
If you say anything that is different than what the dealer wants to do, they are going to be negative. Try calling a couple and just say you want to put in synth motor oil at your next oil change. The ones that don't stock synth motor oil are going to say its a bad thing.
If the ATF is good any "real" test is going to show that. Any real mechanic is going to be looking for old, low, dirty oil. Being that T-IV is meant to out live your warranty, its really unlikely that it would a maintance issue to begin with.
Surely there are people out there driving around with quick lube ATF brews from DEXIII (lubeguard, etc) who think they got real T-VI. I've never heard of any denials of warranty for someone that had what was suppose to be a compatible fluid in the transmission. And guess what, if you buy a third party extended warranty (not a toyota warranty) your more likely to be pushed to an AAMCO or other garage that loves to use these lower cost DEX converted brews.
Honda Z1 is a good example of people not knowing what they have. The real deal doesn't have phos (see a recent VOA). If you look through the Z1 UOAs look for that(I found at least one - the poster mentioned that he had the AT flushed at some chain auto store. He thinks he has real Z1.). Looking at UOAs for Amsoil and T-IV, nothing really stands out to me like Z1 does.
I don't see how its going to be an issue with the strong support from Amsoil. I really doubt Amsoil would not come forward. Think about it. A few postings that Amsoil doesn't support its ATF - thats big time damage. Nothing speaks worse than NEGATIVE news - a 4000 dollar transmission is pennies relative to the damage negative stories would have. Toyota would have more luck trying to say that you somehow added the fluid incorrectly (over fill, under fill, backflush etc)
.......I'm not sure when all Toyotas moved from DEX to T-IV, I know the trucks did it in 2003. I looked at the difference in one transmission from 2002 and 2003, I didn't see anything that stands out. It appeared that a band or two was enlarged, but I think that was to improve pre-mature failures. I have a hard time believing that the 2003 transmission was engineered for T-IV - I don't see how they could have planned that far in advanced. I do believe they fine tuned the AT for T-IV, but I don't believe it could be significant. Toyota probably was more driven to keep money from GM.