My local dealer is awful (Autonation Toyota Arapahoe in Centennial,CO)....they are unable to locate a part # for inverter drain plug gasket. In fact...they tried telling me there isn't a drain plug at all Anyway....before I sift through dozens of part #'s online, I figured I would ask the group first. Thanks in advance!
As a wise man once said: it is better to have and not want than to want and not have." To the OP's question: I will be changing my coolant soon. Momentum Toyota of Fairfield,ca gave me the same response, but I was able to find the part number ( see the pic). I think both total were $5, so good piece of mind. Good luck with your coolant change!