"I am not 100% sure of this, but I think a lot of modern breather valves are one way - the open to release pressure as things heat up. When stuff cools down, they close off and you get negative pressure (well its positive but less pressure inside the axle than outside air). Generally this is okay as things heat back up and build pressure again when being used. And, of course, and 1-way breather valve can fail or be gummed up with mud and dirt - but if the axle is hot it should be okay if you are not submerged long enough for things to cool and begin to reduce pressure. In other words, don't park in the deep water.
There are two-way valves as well - such as mine - and I do a lot of water crossings without issue. I do try to change my fluids at the end of any wheeling season where I know I have done some deeper crossing - and I have never found any significant water indicators.
Another point - if the breather valve is plugged or not operating properly, then air pressure differences may begin to force air around other seals and begin to cause fluid leaks etc. Plus, if those leaky seals are lower/closer to the ground, then they have the potential to be below waterline for shallow crossings where the breather might normally be above the water level.
In this hobby, frequent fluid changes and maintenance is often done based on where you have been, and in preparation for where you will be going, as opposed to how far you have driven. That being said, I am much less dedicated to my toyota maintenance than the old cj. New 4x4s are generally pretty impressive in all aspects of reliability, capability, durability with minimal maintenance in the big picture."
There are two-way valves as well - such as mine - and I do a lot of water crossings without issue. I do try to change my fluids at the end of any wheeling season where I know I have done some deeper crossing - and I have never found any significant water indicators.
Another point - if the breather valve is plugged or not operating properly, then air pressure differences may begin to force air around other seals and begin to cause fluid leaks etc. Plus, if those leaky seals are lower/closer to the ground, then they have the potential to be below waterline for shallow crossings where the breather might normally be above the water level.
In this hobby, frequent fluid changes and maintenance is often done based on where you have been, and in preparation for where you will be going, as opposed to how far you have driven. That being said, I am much less dedicated to my toyota maintenance than the old cj. New 4x4s are generally pretty impressive in all aspects of reliability, capability, durability with minimal maintenance in the big picture."
My 2012 JK has rubber tubes attached. The front runs up into the engine comartment way above the top of the wheel wells. Back I believe goes up by the gas filler tube.