 So transmission fluids have tremendous amounts of detergents in them and they clean as they go. As fluid breaks down, it can no longer clean. And it starts depositing little pockets of crud everywhere. And that's completely normal. Now, when you flush out your transmission, you flush out all of that old fluid that can't clean and you put all brand new super strength cleaning fluid in there. And if you've been on top of your maintenance, there's not a lot of debris in there.