All mechanical boxes with oil that expands and contracts has to have a vent of some sort to prevent the seals from blowing out. I don't know why you are asking about the type of vent but it leads me to believe that there is something wrong with your Rio tranny and it involves pressure of some sort. --- I'll go out on a limb and say that your gear box has a separate vent because if it used the dipstick, it would pop it out of the tube.
kind of was thinking the same thing,now need to find out where box vents.retried new gasket as well as rtv sealant,still leaks at pan.
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