I'm approaching 100K on my Tacoma 2.4L 4AT and I wanted to know what the maintenance freaks at BITOG suggest. The manual says it's lifetime fluid (top off with Toyota ATF D-II or DEXRON III/II). Change only under severe duty. I just use it as my commute vehicle and rarely ever haul heavy stuff although I used it to move a lot of stuff a few times. Should I: 1)Leave it alone, it's says lifetime fluid. Toyota knows more than me! 2)Flush and fully replace with a synthetic like M1 or Amsoil. 3)Start a drain and fill routine every 10K miles to keep the fluid fresh. Feel free to add anything else I should do.