[bepperb]

There isn't anything really special about the T-IV, as opposed to the WS which is much thinner than anything aftermarket. I've heard a lot of long-term positive experiences with people using both M1 and Amsoil universal synthetics over at BITOG, and recently Castrol has a Import ATF for T-IV and Honda's Z1 which some people have started using and seem to like but hasn't been around long enough to give a definitive thumbs up.

At 40,000 miles I did a 4 quart drain/fill with T-IV, and at 60,000 I'll be doing the same thing with M1 and transitioning to that over the next few OCI's. The M1 cost less and is a better oil than the T-IV (also made by Mobil). Whether or not the M1's friction characteristics are similar to T-IV only one group knows for sure, Mobil employees, and they have M1 ATF recommended for replacement for about two years now.

To be honest, just changing it with either puts you way ahead, and T-IV isn't very expensive (about 4 bucks a quart at my dealer).

Of course, now for the barrage of people who know you can never be wrong writing a post saying to stick with OEM.... If anyone actually has a negative experience using a substitute for T-IV, I'd love to hear it.