Inverter drain still leaking even after Recall on inverter pump

Hi

I posted a few months that after replacing my inverter coolant that the drain plug leaked.
I tried to tighten it but that did not work. New Alluminum washer was installed

I took it in about 1 month ago for the steering shaft and inverter coolant pump replacement.
After they drained the system and refilled post inverter pump replacement It still leaks.

Do I need to replace the drain plug or do I have a crack in the casing
The Alluminum washer has no gasket material on one side. Is this correct
I've seen both types on various engine oil drain plugs. I thought of permatex also

Thanks for any guidance.

Greg

 

Turns out when the recall was done on the inverter pump the dealer did not drain the fluid they just pinched off
the rubber lines going to it. So I drained the system and replaced the aluminum washer VIOLA! no leaks

Greg