That is very interesting, I agree entirely that any fault (I am an ex Aircraft Technician) no matter how small or apparently insignificant at the time, as soon as it has a direct link to safety (brakes - tyres - suspension -seat belts etc) should be treated with the utmost priority and caution.
Indeed, in the case of my seatbelt I will be asking for a front pair including pax change under warranty, and I will confirm in writing that if the lesser used back ones should fail in the future (or show signs of not functioning properly) they too should be replaced (regardless of warranty status).
This has been an interesting exchange thank you all, I have to say that LEXUS have come to the right decision albeit a little late. I guess I was the first here at LEXUS Reading to report the problem but future concerns will be dealt with in accord with my outcome. I still thing LEXUS Reading folk are extremly good. :D :D