Took my FJ back to the dealer yesterday for the 5,000 mile oil change. Changed out the oil for Amsoil SAE 0W-30 Synthetic Signature Series Oil, Amsoil EAO57 Oil filter, fluids in the front differential, rear differential, and transfer case were replaced with Amsoil Severe Gear SAE 75W-90. I had the mechanic check out the old oil in the rear differential. It looked a lot darker than the oil in the front diff. He told me that is normal, the oil in the rear diff is always darker and it also contains a small amount of metal shavings on the magnetic plug. He also said that if there is a problem like excessive wear the oil would be a lot darker, more metal shavings but the big difference would be in the odor of the oil, it would really have a bad smell to it.