I happened to have a friend of mine take a look for me under Harlem at something earlier this week … (I’m way too big for ever doing that, at least at tire jack stand level 
) … After he was done looking at it, he rolled out and said, "I kinda hate to tell you this … but you need to know … " 
He broke the news to me as gently as possible that she has RUST on her front floorboards … In some places, it was all the way through the metal … In fact, he said on the driver’s side he could actually see the black mat/carpeting peeking through some of the holes.
WTH??? 
I knew I had a very small area of rust in the wheel arch on the right rear quarter panel, but I attributed this to some kind of body damage (in the past?) that was poorly repaired, or some other damage in that area that let rust in … I had no idea she had rust in any other body area (again, one of those Ebay sellers that didn’t list ALL photos of the car or mention it 
). I’m stunned that a '00 model XJ8, which supposedly had Jag’s top rustproofing techniques used on it to that date, nevertheless allowed that to happen, and in a period of less than 20 years. I know it couldn’t have started down here in N TX in the 5 or 6 years that I have owned her, as we are known for NOT having rust issues with our cars in this part of the country. 
True, she was originally a 'noreaster car, spending her last few years before coming to me in NYC (hence her nickname). But still, I would think Jag’s rustproofing should have prevented that from happening even with brutal NY winters 
. 
Can someone please explain this to me?
At this point, I am seriously considering selling or just scrapping her. I’m thinking if I want to keep her and fix the problem I will have to pull her front carpeting and mats, coat the floorboards in that area both from above and below with “rust converter/reformer” (or that POR stuff someone mentioned earlier), and then smooth over/fill in the holes with that metal gauze tape + either solder or using metal-added Bondo, before putting the carpeting and mats back in. That’s assuming that kind of repair will suffice, i.e. if her floorboards are not too badly weakened by the rust. If they are, then it would look like cutting the floorboards out completely and welding in “new” ones are going to be required, which will be high $$ 
, I’m sure. 