Your Lexus’ engine oil is not the only fluid that should be maintained on a regular basis.  The transmission, differential and transfer case (if four wheel drive) lubricants should also be replaced regularly. Each of these components has  internal moving parts and the lubricants that offer protection will lose their protective qualities if not replaced.  Some of the newer models have long life fluids that don’t need replacing as often.  Please call for information on your particular year and model.