Don't tell them anything, you don't know for sure it's been abused and giving them that idea will give them justification to deny the warranty work. If the trans was fine for 9k miles and just started happening it's just warranty work. Why would this be abuse from a previous owner that might of abused it.

They did, one of their techs said the transmission was bad, then they said Toyota wants to send someone to inspect the transmission to see what exactly is wrong with it, but I still needed to authorize them to put down the transmission. They service rep told me not to worry about it though because it's pretty rare for them to deny the warranty.

Hope it works out for you. You're just a car owner with a bad trans. That's all they need to know :)