I have '07 SR5 with V6 4x4.
At 15K factory fill in rear diff looked very dark.
I changed it with non-syntetic Valvoline 80W90, took close to 4q instead of by the book 3.2q.
I didn't check front diff or trabsfer case at that time.
Fast forward, I am at 30K mi now.
I checked tranfer case and oil...
