Just bought my 1st Lexus, a 99 RX 300, a few weeks ago. Not sure if the blades have been replaced before, but found they took the same inserts as my 97 Accord. Over the years, I found my best inserts by LEXOR, available at your local Wal-Mart. Type D fits the driver side and Type B fits the passenger side and the rear. Yes, the rear! You do need to cut them into your sizes.
Try them out and let me know how you think about them. One thing for sure: they are easy on your wallet: $5 per package of not just one, but TWO inserts!