My mechanic also tells me I'm fortunate that my DS is a five speed manual. No semi-automatic gearbox for me. Also makes the engine bay a lot more accessible (although it is injection). So far, I've replaced the headgasket, cylinders, water pump and injection distributor (with one that achieves lower revs in neutral). The engine repairs were substantial, since water had leaked into one of the cylinders, but it was possible, and now it just starts when I turn the key.
My Xantia is the Activa V6 model. That ES9 engine is a beast. I've been told that it's usually the car, not the engine, that breaks first with those ones. But really, what I was more interested in was the Activa suspension. It feels like driving a go-kart, yet with the suspension of a Bentley, and the practicality of a hatchback. I know they were trying the same sort of anti-body roll for the DS back in the 1960s, but money was always running out (unfortunately, I cannot seem to find the pictures, I know they exist online somewhere).
I intend to keep my Xantia around for a long time. Took it to the US once, and drove from coast to coast and back again.
Activa V6 is amazing, those are super rare to begin with and I've only driven one once. Cornering in that thing is the weirdest experience initially and afterwards every other car except for high end sports cars feel 'off'.
DS with a five speed manual is the best combo, keep an eye on your steering housing (those tend to go slowly but failure is potentially catastrophic) and front carrier arms, the bushings will wear out and then you'll start to eat tires. Other than that, your main enemy is chassis rust, everything else can be fixed.
My understanding is that only 2700 Activa V6 were ever built. I doubt half of those have survived. Now and then, one will appear for sale, and they disappear about as quickly as they appear. I remember rushing across country to pick up mine as soon as it went on sale.
I've recently bought a house with room for a workshop. I've known for a while that the steering on the DS was an issue that needed fixing. Now that I will finally have room to work on it, I look forward to start fixing this among other issues. Including fixing the wiring for the thermostat to the dashboard.
Fixing the steering on a DS is a major operation, make sure you get the shop manual and if you can practice on a junker before doing it on your real car, it is probably one of the most labor intensive jobs you could do on that car.
Rebuilt units can be bought, they're better than the originals and should last the (remaining) lifetime of the car, I would definitely recommend against trying to rebuild one yourself, they are super finicky to work on and require a ton of specialist tooling (and experience) to do the work properly.
Note that there are right and left hand drive versions of these. Also there typically is a charge if you don't give them your old one for rebuild in return after you've completed the transplant, and, of course there is a huge difference between the 'red' and the 'green' version, which has to do with the sealing materials used, the 'red' system uses a hydraulic oil which is extremely corrosive.
Obviously, after replacing the steering housing you'll need to have the car aligned again, and while you are at it you may as well replace CV boots and ball joints since it is mostly just the price of the materials at that point.
Fortunately, I have a "fixer", who is extremely familiar with these vehicles (it's basically all he does), so he would be able to get me some proper units, and would be well aware if I am being overcharged. Indeed, just looked at his site (that I built for him), he does have a replacement unit for sale for ~800 euro (with VAT).
Good! Have fun, you'll learn more about your DS than you ever wanted to know. I've rebuilt a DS bit-by-bit while it was in use and I would have much rather had the time to do things in a more planned manner. Engine rebuild is a nice chapter in its own right, the 21 is the best engine and you could get a junked engine and rebuild that at leisure, they are very doable.
My Xantia is the Activa V6 model. That ES9 engine is a beast. I've been told that it's usually the car, not the engine, that breaks first with those ones. But really, what I was more interested in was the Activa suspension. It feels like driving a go-kart, yet with the suspension of a Bentley, and the practicality of a hatchback. I know they were trying the same sort of anti-body roll for the DS back in the 1960s, but money was always running out (unfortunately, I cannot seem to find the pictures, I know they exist online somewhere).
I intend to keep my Xantia around for a long time. Took it to the US once, and drove from coast to coast and back again.