I don't have a Lexus... huh huh.... huh huh....., but recently became damn near an Oxygen Sensor expert and this is the ONLY place.. and I mean the ONLY place on the web I have found the same question that I posed: "Can someone tell me what part of an oxygen sensor wears out?" - Recently I was SURE.... would've bet my life on it that 1 or more O2 sensor(s) were bad so I went out and bought all 4 of them and replaced them and the vehicle acted the same way (bad idle and bad MPG). To my disgust after all that hard DIY work I pulled the new sensors out and hopefully will get my money back for them.
Here's why I chimed in: The question of "what wears out in an O2 sensor" indeed is a good one. You would think the element that senses the air/fuel mixture would over time wear out, but it is a solid state chemical reaction that takes place and the element will always be present short of your car's exhaust reaching LAVA temperatures for extended periods of time. As long as the solid piece of element still "exists" underneath the sensor guard it will still REACT when in use and most modern day sensors begin reacting almost immediately cause they are self-heated.
This lingo "wears out at 60k or 100k miles" is simply due to the fact of which I have found repeatedly when dealing with electronics or machinery. PEOPLE DO NOT WANT TO REVIVE AN OLD PIECE OF HARDWARE. THEY/WE LIVE IN THE DAY AND AGE OF..... GET A NEW ONE... ITS FASTER AND EASIER. So then people start saying (because of laziness) that things "go bad" or "wear out" assuming no one wants to take the time to actually "FIX SOMETHING" instead of replacing it. FASTER and EASIER? Well, that all depends on how you look at things. The old saying "If it ain't broke don't fix it." pertains EXTREMELY well with O2 sensors cause short of them being physically damaged all they usually need is a good CLEANING. The only other part of the sensor that is questionable is the ceramic inside it, but as long as the sensor body is sealed I don't think I'd ever worry about it cause its just used for heat transfer.
The posts are rarely seen about cleaning the O2's because everyone "believes" the industry's verbiage so they can continue to what..... whats the magic words.... yes..... "MAKE MONEY". Pull your O2(s) out and clean'em! REVIVED for another 60k - 100k miles just like that!!! The safest method I've seen and done myself is using CRC electronic parts cleaner (picture of alternator and starter on the spray can) and you could probably use MAF cleaner as well as thats even more sensitive. I power sprayed mine clean and then soaked them in the CRC electronic parts cleaner in the little caps that come over the sensor to protect it. You could also use a small ziploc bag I imagine or a small container... small enough to fill up covering the sensor element only. I let them soak for about 2 hours. Pulled them out and power sprayed them again to get rid of loose debris and I did see debris come out when I initially pulled them out of the soak. I let them dry overnight before reinstallation. I have since reinstalled them and I have NO check engine light. I have not driven the vehicle yet though or let it run for more than say 5 minutes because I have exhaust work to finish, but others have done this method with great success.
Here is another tip: O2 sensors BREATHE!! If the TOPS of the wiring harness of the O2 sensor is full of dirt, sludge, debris etc... the sensor will NOT function correctly. Newer sensors breathe through the small gaskets surrounding the wires and use outside air for comparison to the air in the exhaust pipe. Older O2's use a breather port which I've never seen, but have read is on the side(s) of them. If ya don't wanna pull your O2's out a simple check to see if they are dirty on top where the wires go in and a spray with the recommended cleaners may help your engine run better.
Lastly, a friend of mine on another forum I'm on replaced all of his oxygen sensors cause "he thought he should due to the big recommendation in the sky as preventative maintenance" and observed ZERO MPG change. It should also be noted that OBDII vehicles 1996 and above are much less subject to needing O2 sensors replaced because of how well the computer manages air/fuel mixture over time. Pre-OBDII vehicles dirty sensors faster, but again I would bet you could just clean them and reuse'em.