I used Valvoline gear oil VAVOLINE 80w – 90 GEAR OIL (conventional) in my 2005 4runner. They had no synthetic where I am.

I did the first ever Drain of three quarts at about 145,000 miles and plan on doing another after another 70,000 miles.

The interval of 30,000 miles isn't necessary IMO, but won't hurt.

I do no towing and no high-speed driving, and over 50 mpg seldom

My diff fluid was ok but black.

Someone posted that differential fluid doesn't ever need service, but I don't know about
that.

I've read some posters go 275,000 miles and never changed the rear differential fluid.

LIKE THIS POST below..

"I've seen many axles live past 300,000 miles on the original lube, but the stuff smells worse than dead dinosaurs should. It's enough to make most guys gag."

He didn't say these differentials had failures.