oxygen sensors

NGK NTK 24044 O2 sensor. Made in Japan. New unused. I opened one box just for photos. $150 each, two available.

My FJ62 is throwing codes 25, 26. CEL comes on after warmup and driving after 5-10 miles. Other than the pesky CEL light, engine seems fine. I hooked a digital volt meter to Ox1 & ground, and also Ox2 and ground, and got a steady voltage swing from about 0.1 volts, to .9 volts around 1 cycle...

I have two DENSO 234-4520 Oxygen Sensors for 93-95 FZJ80 Unopened, in box, sealed in plastic. Bought from Amazon for $190/each + tax (about $210 each in California) I sold the truck before installing them, and still have them. $350 obo shipping included.

Just mulling it over, over morning coffee, if my O2 sensors need to be swapped out after 298,000 miles? I don’t have codes telling me that they are bad? But do they become inefficient after so much time and mileage? Should they be changed out just for the heck of it? It came up because I did a...