I have a myriad of things wrong, the only common item is the body ecu, according to my wiring diagrams and symptoms. For example, the lights for the stereo panel don't work, ditto the ECT switch light, transmission gear light, dome light when you open the door (it works fine with the dome light switch) and cigarette lighter. The automatic headlights will not shut off automatically after I get out of the car ( I killed my battery one night expecting the lights to go out after I put the car in the garage). The key in ignition chime doesn't work. The driver's seat belt chime doesn't work. The climate control keeps resetting to 75 degrees over night.
I have a listing of programmable features in the body ecu, it controls most of these items. I would try to program these features but the Lexus Technnical Service Information system (the one you have to pay to use) says you have to have a "Lexus hand-held tester" to program the ecu.
I did find a recall of the ecu for some 99 RX300s that involved replacing the ecu. There was a problem with the automatic headlights and the tailights failing to operate at times. The recall contains instructions on how to get to the ecu to replace it and then reprogram the new one to recognize the car key. That's why I want to find a used one to try as a replacement. Lexus would probably want a fortune for a new one.