I've done plenty of really long trips with it (many thousands of km), but I did replace all of the accessible high pressure LHM tubing at some point to get rid of the periodical 'Arret!' light on the dash because the system lost pressure. I can also tell you from experience that trying to drive a DS without pressure is both an art and a body building exercise at once.
Xantia is a great compromise between 'modern' and 'old fashioned', a bit plasticy but the one I had I drove into the ground over many 100's of thousands of km. The final nail in that particular coffin was to lose the headgasket somewhere between Munich and NL and just continuing the trip, it even got decent fuel economy but it wouldn't start up after being shut down and once we looked into the engine it was declared a miracle that it made it all the way back. Great car, all around and given the distances covered ultra reliable.
The real problem in the DS model is the semi-automatic gearbox which is super finicky regarding hydraulics levels (you'll notice a ticking sound when it is trying to engage and can't quite make it due to a lack of fluid, you can temporarily fix that under the hood by forcibly actuating it but driving it like that is really not recommended. Nor is driving it when one of your drive shafts breaks and you block up that side of the drive train. Nice low engine revs though, we jokingly called it 'economy mode'.
I also had an ID-19, a simpler but altogether far more robust car.