I put transmission fluid in a 97 ford expedition and water is somehow getting in.why is this?

I put transmission fluid in a 97 ford expedition and water is somehow getting in. Why is this? - 1

Transmission cooling line runs through the cars radiator. Means like at leak in that line. If you find ATF in the radiator then the radiator will need to replace; or somehow fix the broken line which usually it is not modular.

Transmission gets cooled by separate tank on the side or bottom of the radiator. That tank has rusted and now mixing with water/anti freeze. Radiator needs to be replaced. Now the transmission if caught early enough needs to be flushed. If not the water/anti freeze mix will ruin the transmission and then the transmission will need to be rebuilt