Radiator fluid, differential fluids, transfer case fluid, transmission fluid, and brake fluid are all fluids that you can replace. The radiator fluid is located (hence the name) in the radiator and in the motor. You can replace the radiator fluid by removing the lower radiator hose and just doing a drain and refill, or you can take it to a shop you trust that has a coolant exchanging machine and have them replace all of it.
The differential fluids are both GL5 gear lube. The differentials are the pumpkin looking center sections of your front and rear solid axle housings. Most multi-grade viscosities will work. Conventional 80W-90 will suffice unless you have a differential that is limited slip or "trac-lock" as Jeep calls it. This will requite either a synthetic or an additive specifically intended to condition the parts of the limited slip so that it will work properly. You can use a larger range viscosity (i.e. 75W-140) if you tow are put larger amounts of strain on your vehicles differentials. It's not necessary, though if you don't want to spend the extra money.
The transfer case will probably take an automatic transmission fluid such as Dextron III/Mercon. You'll need to check the tag on the transfer case to see which model number it is and what fluid it subsequently takes. The transfer case is attached to the back of the transmission and has two drive shafts coming off of it going to the front and rear differentials.
Assuming you have an AW4 automatic transmission, it will take 3 quarts of Dextron III/Mercon ATF fluid if you just drain and refill it.
Replacing brake fluid isn't really a high priority most of the time, but it can get dirty and need to be replaced. Most people just do this around the time that they do a brake job as it makes more sense. They basically need to be bleed until the new fluid that is being added starts coming out the bleeder valves.
2012 Jeep Wrangler Rubicon Unlimited in Dozer (stock)
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