Hello. I also have a 98 ES300. There is an automatic transaxle differential that is to be filled separate from the automatic transaxle. The diagram I have shows the drain plug facing the ground (as it should). The bolt you have to unscrew (and use a syringe or gear oil pump to add ATF) is several inches up to the side facing the driver's side door. After draining, you add the ATF until it just starts to seep out of that fill hole- then tighten the plug. The recommendation is that this differential lubricant is changed every 15K, whereas the automatic transaxle lubricant (both ATF) is changed every 30K.