Front, I'd run it. Rear, I'd think about new gears. The rust runs into the the center of the contact patch and could cause a groan noise. Is there a backlash change when that part of the ring gear is in contcat with the pinion?
Was the differential full of water for a long time without moving the gear? It looks like it from the rust "line" across all the teeth.
2004 4runner just starting to build
83 Hilux SR5 is being sold
94 pickup in a pile of parts