I was lucky. I didn't buy my car from Lexus. I spotted the issue within the first week of ownership. The dealer agreed to put the car right.
I'm confident, but hopefully wrong, that a Lexus warranty won't cover this. Reason being that I had an IS-F back in the day, and it developed a clicking seat (when cornering). Once again, this was a rail issue. I tried my best to get Lexus to replace the seat, but even going to Lexus UK, the answer was, "Sorry, that's wear and tear". I guess, if your car is very low mileage, things might be different. Like I said, I hope I am wrong.
Technically, I do believe Toyota make their seat mechanisms out of chocolate!