On 3 Aug 2018 19:34:47 GMT, Clare Snyder wrote:

What pressure??

Well, something is pushing the exhaust out the tailpipe.
But I get your point that it's likely in the low psi range.

If the cats are good your exhaust pressure should never excede about
2.5 psi, at any speed or load.

OK. Well, at 2.5 psi, that oxygen sensor is just fine with respect to
leakage then, since the last 1/8th of a turn was tight.

Take a piece of vac hose or fuel line - stick one end in your ear
and the other down by the sensor.If it's leaking YOU WILL KNOW!!!!

I have a mechanics' stethescope. I still can't hear all that well (too many
explosions in my early days).