I brought an LS400 in Oct 02. It had 86K on the clock with full service history and I had 4mths Lexus warranty left on it. The rev counter needle needed to be replaced under warranty at my local dealer. They gave excellent service and collected,returned and valeted the car--- what more do you want. I also got a service done -- £225, not bad.
I would say you need to buy with a full history. Don't forget that 20mpg is about average and a tank will cost over £50.
Regards
Jay