I took these images as I worked with Lunt instructions.
An eyeball/ruler measurement of the old orings to compare to the new orings was of no real value.
The old red "outer oring" appeared slightly larger in diameter than the new black 34mm oring supplied, likely from stretching but still of no value to compare.
The old red "inner oring" showed what looked like a split line, the result that became immediately obvious as it was removed.
The old red "inner oring" was definitely thicker than the old red "outer oring"
I have used option 3 from Lunt and put the black 32mm oring on the "outer groove" and the 34mm on the "inner groove".
Is there a difference when I screw the pressure tuner cap onto the brass tube, well yes, I think I can feel a difference but the real test will come I guess when I get to try it out, possibly this Friday due to weather.
What am I expecting to see? Dunno will let you know!
Here is the Lunt link showing the steps to where I got to before posting this thread.
https://www.youtube.com/watch?v=tsEgUI9Wtaw
Faye's explanation was indeed very helpful as were all your inputs here and hopefully my experience will assist others.