I have owned a 2005 and 2006 Scion Xb. On both vehicles, the transmission cooler in the radiator busted at 130xxx miles and 210xxx miles respectively in 2022 and 2023. The transmission fluid and coolant consequently mixed and it was a nightmare to get all of the transmission fluid out of the coolant and coolant out of the transmission fluid. Of course, the radiator had to be fixed, and I did all the work myself. The mechanic at my shop thinks that it's a defect with the radiators, something worth looking out for if your transmission starts acting weird! Thank God, somehow the transmission is still working decently, with slightly reduced performance in shifting at times.