I realize this is an old post but it helped me find the problem with my daughters 2000 RX300. Floors were completely soaked after a few days of heavy rain. I drew the sunroof back and on the passengers side of the "sunroof well" there was a standing pool of water and not on the drivers side. I ran some weed-eater nylon down the drainage hole and the water drained away out beneath the car. I poured more water down to be sure and it drained away too. Very helpful. Thank you.