Changing the fluid in a transfer case is not necessary under normal operating conditions. The only way to drain the fluid from the transfer case is during the transfer case disassembly procedure. When reassembling the transfer case, add 1.3 oz. (38.4 mL) of API grade multipurpose gear oil GL-4 or GL-5 of the proper viscosity. Use SAE 75W-90 or 80W-90 oil in all models to refill the transfer case.