Yes i have the extended warranty, they tried to charge me for the rad at first (£300), found out from a member on here that Rads can be damaged when the headgasket goes so i told Lexus to go speak to the warranty company, which they did and hey presto its covered.
I think the dealer try to get the customer to pay for work at first as its easier than trying to get the warranty company to pay out, but i could be wrong.
see my thread here http://www.lexusownersclub.co.uk/forum/index.php?showtopic=80791 Steve2006 explained it to me.
Good luck pal.