Just make sure that the dealer aligns your headlights after they are replaced. I had both of my headlights replaced under warranty not becuase they were leaking, but because they were cracking!
After they were replaced, I had to go back 2 times to have them realigned. After the second time they couldn't do it for some reason so I did it myself.
I have a service manual for the IS300 and took the information to align the headlights (dimensions like where the beam is to be etc.) and had a guy at work plot it on a CAD program, printed it out 1:1 and placed it in front of my car to align the lights. Let me just tell you that they light up the road WAY better than what they were intially aligned at from the factory. I think some Lexus technician don't know how to do it properly, so do it yourself!