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In one of the quoted passages (fourth paragraph, or the first large paragraph), it states, "...since the trans line pressure is much greater than the cooling system pressure, when the cooler fails it is usually a one-way valve and sends atf into the coolant...."
This is not so, at least most of the time. If you have ever done a transmission fluid "flush" using the hose technique (e.g., using IPD's kit hose), you would see that the ATF pressure is low. The pressure gradient (ATF versus coolant pressures) depends on the state of the engine:
When you first start up a cold engine, there is little coolant pressure, so the ATF pressure, although modest, is greater.
As the engine warms to normal operating temperature, the coolant pressure also rises, and soon far surpasses the ATF pressure. And this gradient, in this direction (i.e., higher for coolant and lower for ATF) increases further after shut-down, when there is zero ATF pressure and the coolant remains hot and pressurized. Only when the coolant has cooled to ambient temperature will the coolant pressure also drop to zero and equal the ATF pressure (also zero).
And then, when you start up the cold engine again...[back to the beginning].
So the majority of the time when there is some pressure gradient, it's the coolant that has the higher pressure -- ATF pressure is greater only for the short time the engine runs until its coolant warms up. And so one would expect a greater transfer of coolant into the transmission fluid than vice versa -- as well as doing the worse harm, as the cooling passages can tolerate some ATF far better than the transmission can tolerate some coolant.
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