Advice I pass water to automatic transmission

Okay, buddy... the first question is, how did the water get in? Otherwise, it's going to come back... all right

Well, it's simple, the water only got in through one point.
The only point where it could have entered was through the water radiator, since on one side where the radiator cap goes there's a small oil cooler that comes from the transmission. If you put in an external radiator, which is cheaper, you separate the water from the oil, and that way there's no other way for water to get into the transmission.