If I am not mistaken, what has happened in this car is that incorrect brake fluid has been replaced in the circuit, and this has caused the decomposition of the rubbers of the brake pump seals.
In the first place, if there is no absolute certainty of what is going to play in security organs and there is no "mechanical friend to open" the only exit is to go through the workshop.
Secondly, the brake fluid "does not disappear" without leaving a trace, with this I mean that if you ever see the brake fluid a little low but within the min and max limits, you should not fill !! Because the only thing that happens is that the liquid is in the brake tweezers due to the natural wear of the pills.
In this case, when pills or discs are changed, when opening the tweezers, the liquid level will recover its level. (Max when new pills are).
If we fill, what we are going to get is that the brake fluid deposit overflows and that the paint near the brake pump is lifted.
OOROTRA SOCKER !!! The brake fluid of "normal" cars is DOT 4 or DOT 5 brake fluid according to DIN 1703 regulations, synthetic orygen and light yellow.
Some Citröen brand cars use green LHM fluid and mineral origin and others use ATF Dexron II. Red liquid and mineral origin.
Both green and red liquid are totally incompatible with brake fluid, and are only used in some models with centralized suspension and brakes systems (Citröen, Mercedes, Audi ...) and not all of those brands.
For more information are always those of spare parts, the same ones that the pills sold you for 55 euros should know that your car carries such fluid for the brake, such antifreeze, such oil, such filter ... So when you have doubts ask first, you will save many euros.
The brake fluid has a half -year life of two years or 100,000 km, like the engine antifreeze, although I know a lot of people who do not change one or the other ... (then what happens is something of each one). In principle, the liquid can endure more time if the car brakes are not required much, but it is advisable to change it at most to 4 years.
I don't spread anymore. All the best.