Having recently had 2 o2 sensors go i did a lot of research to find new ones.there a lot of 'universal' ones out there-dont go there!!.i used a company ECO LAMBDA ,THEY SELL ONLY O2 SENSORS and are very helpful,they can be found at
My linkspeak to Graham. the part numbers for my 2004 ls430 are: f/left 8946550130
f/right 8946550120 ,both rears(post cat) 8946550160.got these from lexus .hope this helps