Drain and refill fluid substitute for Toyota WS?

I’m new to the world of servicing automatic transmissions. I just bought a 2009 Scion with the U241E four-speed auto. It has 120k miles and I think it’s time for new fluid. The manual specs Toyota WS fluid, which is $$$. For the final fill I will likely use Valvoline Maxlife but I want to do several short interval drains before the final fill. Rural King sells a Dexron 3 equivalent fluid at $27 for a two gallon jug so I could potentially circle a whole bunch of fluid through cheaply. Walmart...

Read more