O2 sensors in Oz

(Richard Dowling, 1979 XJ-S HE+5sp coupe, 1989 XJ-SC, 2003 XJ8 3.5L) #1

This is a 2003 XJ in Australia, 3.5L V8 although on many sites it is referred to as 3.6L.
This model has a very confusing designation since I have seen it described as XJ, X350, and XJ350.
It has flagged an engine malfunction and my scanner indicates fuelling problem on bank 1.
It still drives , although yesterday it went into a limp mode for a short while.

My guess is it still has original sensors and has now clocked up 147,000km.
VIN ends G00689.
About time to replace them, so:

  1. I will at least replace the 2 pre cat ( upstream ? )

  2. Is it worth it and/or needed to replace the 2 post cat ones ?

  3. One local non Jaguar source quotes A$320 and A$200 each for them ( US$220 & US$140 )
    First one is part O2SEN-1186, does not state manufacturer.
    A second local source has sensors around US$70 but does not show one for my VIN, although I could contact direct and see if they do have suitable ones.

  4. Do they sound like sensible prices, they seem steep to me.
    On Ebay similar DENSO pre cat start from around US$70 out of UK
    From China they start at US$25, brand unknown.
    I expect there are very few variations in sensors and I would be surprised if auto companies pay more than US$20 each for them. The big variation might be cable length

I think this should fix the malfunction, but even if it does not I reckon it is a good strategy at 15 YO and 147,000km.
Any suggestions welcome.