Successfully replaced the plate a few days ago - the plate comes with a drain plug already installed. Used and let it cure overnight. Then filled her up with fresh coolant - no leaks. Did not even need the Techstream as the coolant pump started right away with ignition.

Here is the old plate with a stuck drain plug. After the inner hex stripped I have also tried (unsuccessfully) to use an air hammer to drive it out - that is why it looks so mashed up.

 

Played with a milling machine today and carefully drilled out the old drain plug. Then resurfaced the plate so it can now accept the larger "outer hex" drain plug. I will keep the plate for the future as I have two cars with this transmission (ES300h and Rav4h) and may need to swap this plate again. The original and the "upgraded" drain plugs are shown for comparison.

 

great job great mod .you have now the real plug that should be on lexus drain.on mine Rx 450h somebody put drain plastic valve on the hose and it is possible to service coolant via that valve I have posted picture in my other thread so you can see it.

 

I changed both the engine coolant and the inverter coolant in my 2014 ES 300h today. The car has about 120k miles. Two observations:

1) I could not put the car in maintenance mode. I just turned the heater on high and the engine kept running. I was able to bleed the engine coolant just by squeezing the radiator hoses and topping off the radiator. The inverter coolant system did not seem to need much bleeding. I just flicked the hoses going in and out of the circulation pump and that got the coolant swirling in the tank.
2) For both the engine and the inverter I only needed 2 bottles (2 gals) of the Toyota pink coolant. I had purchased 3 bottles and plan to return one bottle after a few days if the level in the filler tanks do not go down.

So the takeaways: 1) Not completely necessary to put the engine in maintenence mode, and 2) Two gals may be sufficient.

 

This video also helps.