The 4Runner is designed to go though over two feet of water without issue. That includes the differentials. I thought all 4Runners had a tube on the differential vents that went above that two feet. Am I wrong?
Just a thought.. not sure I’m right and open to criticism.
If the breather vent is a one way valve/check valve then it should seal shut if water tries to enter.
However the seal is only so good so if you are in deep enough water the pressure may push through?