98 V70 NA - rear o2 sensor no voltage

[Thunderbox]

I am investigating a P0133 code with the following reported by a live monitoring OBD reading. My rear O2 sensor is not reporting any voltage. STFT is reading 50.8%.
The front sensor which was replaced about 6 months ago. It runs about .375 with a STFT of about -3.5 to -2.3 when fully warmed.
Car has 238K with lots of maintenance. I did find a leak in the exhaust post CAT pre sensor which was fixed. I was able to view the CAT from the back side prior to the repair and it looked fully intact. I cleared the code at that time but the CEL came back within a week.
I suspect the rear O2 sensor has failed as I have no record of it ever being replaced.
Any suggestions or ideas?

[db130]

With 238k, I suspect it too is dead. I'd replace it.

I've replaced two o2 sensors with over 200k+ miles on them. I usually take my trusty MAPP gas hand-held torch to heat up the exhaust pipe area around the o2 sensor for about 20 seconds before I try removing the sensor.