Prius Gen 3 Misfire Cylinder 4

My 2010 Prius with 200K kilometers has intermittent misfire in cylinder 4. I replaced all 4 spark plugs with new Denso iridium, Changed the order of ignition coils, cleaned intake manifold especially all 4 tubes within, egr pipe , valve and egr cooler which is a pain to remove and install. Also swith positions of fuel injectors after cleaning them. There is no sign of Head Gasket leak as no coolant reduction.
I had done everything what i could do. The misfire wasn't going away. It came mostly when the engine was hot and at very low rpms infact when gas paddle was not pressed. Took my car to several mechanics but no remedy.
Finally one mechanic said have you changed its transmission fluid. I have not done it said no. He recommended me to chane it see what happens. I opted and took my for a transmission oil change.
To my surprise the the oil was severely dark and only 2 Liters came out. I refilled it with Toyota ws fluid almost 3.8L drove my car and the misfire was gone. I drove 80 kilometers and no more misfire now the car runs smooth.
He said something that Prius has eCVT transmission which requires lubrication to cool the components.