Let me resurrect this zombie topic then. With one sad, and one hopefully happy update.
Sadly, the C5 is gone. I lived in a smaller city when I bought it, with access to a lift and a canal for almost as long as I needed them (courtesy of a friend), and it was much easier to obtain parts from Europe. All three cars in the stable were bought with the same advantage. Life changed, Turkey changed, and I no longer have the time, free access to a lift or canal, and it is practically impossible to import parts as an individual to Turkey now. Obviously, the v6 and Hydractive 3+ specific parts are hard to come by in Turkey (I think mine was the only facelift Mk1 C5 3.0 v6 in Turkey).
The C5 was a victim of sabotage-level "repairs". First, a shop "fixed" the leaking swirl pot. Years later, the thermostat got stuck. I got it replaced. After that, coolant temp always tended to tick a bit above mid point, and I noticed unusual fan noise after I parked from time to time. Since the C5 was always driven sedately, these were not easy to replicate. One year later, climbing Taurus mountain passes under 40C outside temperature, aircon working overtime, with 4.5 people on board and the boot loaded up to the rear windshield, I had to pull over because the temperature suddenly went up. The sensor cap blew, emptying the coolant like a Geyser (luckily nobody was hurt). I had the car towed for around 20kms, had the coolant tank plastic-welded (as the sensor cap is now a citizen of the forests on the mountains), and drove another 80 kilometers to in-laws' summer house. A week later, the car brought me back to where I live, around 700 kilometers and back over the Taurus mountains, only overheating close to the highest pass, as I chose to drive at night and we were much lighter on the way back.
Turns out, the leaking swirl pot "fix" was actually deleting it. If it is not on the car, it can't leak.

And then I found out that the thermostat seal was never replaced. They had just pushed the thermostat in its chamber and called it a day, not bothering to check if it moved at all. The car stayed in storage for many months, with me trying to find a shop that would carry out the repairs by the book. Almost everyone was like "we don't touch v6", and a couple who claimed they would simply stopped answering my phone later, presumably because I asked them if they would replace the head bolts, torque them to spec, and re-torque after a warm up and cool down cycle. Both claimed that was not necessary, they did head gaskets and all everyday, yet one of them didn't even have a torque wrench in the "shop".
Luckily, a fellow Citroen enthusiast volunteered to work on it, and I'm sure he will bring it on the road. But it's one car too many for me at this point. I bought an Audi A3 which I knew from brand new for the wife, as the kid is 10 years old now and our interior and boot space needs are more manageable. We still miss the C5.
As for the Xantia, hopefully she will be back on the road come the end of this month. I found a crashed VSX which a scrapper was breaking, with the 16v engine and manual transmission. And found another shop, which it seems like is much better than the two others I tried before. X1 VSX is very rare in Turkey, this is the only VSX I saw in Turkey apart from mine in the 8 years I owned the Xantia. I bought it in full. Most of it is usable. In addition to manual conversion, I'll strip it as best as I can and keep spares. I'll then hand over the shell back to the scrapper as I don't have anywhere to store it.
Let's see how it comes out and hopefully I'll have photos to share.