I just bought one 2005 in warranty, just aware 2006 is new model would be better. bassic 4yr/50Kmiles,power chain 6yr/70Kmiles. Note CARFAX may not expose all accidents/repairs, it records reported ones. You must test drive! Good luck.
The 2005 GS300 41K miles has one struts leaking and replaced by dealer for free, my shop asked me to replace all four buy dealer defused. So warranty is still limited. A few people told me ext warranty is no use as Lexus has no problem, yet I don't think it is no problem. Anyway after replace it is better.
I just found, rear passenger side power window has problem, if you hold up button it goes up then down! I need to momentarily up the button to close it.
I tried Es350 only 26K miles, not powerful as GS300. I feel, Lexus is ok but not a very reliable car for people want to drive 180K miles+.
I also feel, a warranty even last for 100miles and 1wk will help you to fix 2nd hand problems. I'll start to learn repair because loca dealer charge 90K timing belt/water pump etc. for $24++!