TOkay, you guessed correctly, I had to reply. :-)

What we are talking about here is soldering or crimping connections about 18" from the sensor. Presuming the Walker Universal is the "breathing" type soldering that far up stream would be inconsequential. Further more, Walker, and others, supply heat shrink tubing to go over the crimps. So given a proper and tight crimp and then covered in heat shrink could defeat/restrict the "breathing". I am suspicious of claims of insulated wire's ability to breath the +60" of a Volvo's factory harness, no crimps. Look at the end of the O2 wire at the connector in the engine bay. I don't see any "air passages" and I do see a weather tight seal. So what is one to do?

I like to work from facts and data, and I like to tap the knowledge of experts. My question today to Engineering at Walker Products regarding their Walker Universal 250-23000: "My preference is to solder the connections and enclose the connection with heat shrink. The instructions in hand only speak to the crimp style connection. Any issues or concerns with how I want to do this?"

Walker Products Engineering response: "Soldering connections is acceptable. Make sure there are no sharp points of solder or wire that might pierce the heat shrink tubing. When installing the sensor, make sure the solder joint is under minimal stress, so that it is not stretched or vibrated during driving."

That's good enough for me.