Could it possibly be the sunroof? Looks like there might even be a class action about problems with the sunroof.
http://www.kcrlegal.com/lexus-leaky-sunroof-investigation.aspx
I've been having problems with my leaky sunroof. The dealer refuses to fix it. Apparently I'm not the only one.
http://www.kcrlegal.com/lexus-leaky-sunroof-investigation.aspx