I had the same problem 06 GS430, my dealer told me to call 1-800-255-3987 (Lexus customer service) and tell them about it.
Lexus paid for the rear view, only charged me labor ($150 and change) and comped the mirror. Both outside mirrors were degraded too, they would only go half on both parts and labor for those, but I just bought from Sewellparts.com and put it in myself (super easy). They will only do one of these "courtesies" per car I think, so use it wisely...
Hit me up with any questions.