I had my local indie garage who are also Lexus enthusiasts change the atf fluid in my 2005 GS300 last Saturday. I did a bit of research beforehand and the general opinion was to use genuine Toyota fluid which i bought from Ebay. They could only get just under a litre back in but then started the car and went through all the gear options drive, reverse, neutral and then checked the levels again but it only took the total fill to just over a litre although the book says 1.5l. It has been running fine ever since and the gear change seems smoother unless its just my imagination. My car has done 70k and the fluid had never been changed since new to my knowledge. I also got them to change the diff oil at the same time. https://www.ebay.co.uk/itm/Genuine-Toyota-Prius-Auris-Yaris-ATF-Fluid-Automatic-Transmission-1-Litre/112758271898?epid=651236881&hash=item1a40eaaf9a:g:WfgAAOSwJ71aXdkj