Got my new (used) mirror yesterday fitted etc etc.
Seems from this thread that all our mirrors are the same (heated, electric adjustment, electric folding) and the autodimm was an option.
Although Lexus told me from taking my reg that I have autodimm, my center mirror has the manual lever thing for dimming the glass, and not the button that someone had mentioned here before - thieving gits.
Just wanted to thank everyone for their advice :-D