Maybe I'm paranoid but I've never believed the "lifetime" claim for Toyota's (or anyone's) transmission fluid and would always replace it at some point.
When the ATF is worn out, the transmission’s life doesn't have much time left.
Corrosion inhibitors gradually lose effectiveness. Viscosity extenders wear out. All lubricants degrade with time and use. Pumps chop long molecules into shorter ones.
Transmission Fluid Replacement
in RX 300 / RX 350h / RX 400h / RX 200t / RX 450h+ / RX 500h Club
Posted
When the ATF is worn out, the transmission’s life doesn't have much time left.
Corrosion inhibitors gradually lose effectiveness. Viscosity extenders wear out. All lubricants degrade with time and use. Pumps chop long molecules into shorter ones.