Can you do this with a Xantia/C5/C6 ?

[Xaccers]

I once changed both wheels on one side ,by settting the car on high,putting the jack under ,then setting it to low , but in doing so the car "dumped" a load of fluid What would be the reason for
that ??

Paul...................

Bet you lifted the driver's side right?
Setting it on low returns the LHM to the resevoir.
As the car tilts, it sloshes the now full resevoir and the LHM spills out, especially if you've over filled it in the first place.

[Kowalski]

had a flat tyre on the left back on C5-1
noticed this only after few weeks - it was fine in normal driving - only on motorway I noticed some vibration - like unbalanced wheel.
So I am know what to do if I got any other tyre flat - move it to the left-back and drive home...
I usually drive alone - probably if you have someone on the back seat it will be different.

If the tyre had been completely flat and you drove for any distance at speed, you would have noticed it was flat because it would have disintegrated. A flat tyre on any car (citroens included) will heat up and sisintegrate pretty quickly.