Hello Jim and welcome to the L.O.C.
If you bought from a non Lexus Dealership, then the Salesman does not know what he is talking about.
If you bought from a Lexus Dealership, then he should know better.
Either way, the Consumer Rights Act 2015 requires the Dealer to correct and pay for, any significant problem which occurs within 6 months of purchase.
Remind the Dealer of his obligations to you and let us all know how you get on.
If you bought from a Lexus Dealer then please tell us its name.