The wrong brake fluid may ruin the entire brake system

Check if the 2CV has a front disc brake system. If so, chances are that someone previously used the wrong brake fluid. Not many mechanics know about the fact that the 2CVs with disc brake system can only use LHM and NO DOT brake fluid. So they use the standard brake fluid like in any other car to top up or replace.
Again: All 2CVs with disc brake system ONLY use LHM!
Even a little sip of DOT brake fluid will ruin the entire LHM system (See related article).

When you find the standard DOT brake fluid in the LHM system you have to prepare for an expensive repair. The complete brake system needs to be replaced. Calipers, master brake cylinder and wheel brake cylinders in the rear must be replaced. Mostly it is recommendable to replace the brake shoes, rotors and brake pads as well since quite often they deserve to be replaced anytime soon.

Beware: If you have a LHM system with DOT brake fluid in it, it's not enough to flush the system with fresh LHM. The DOT brake fluid dissolves the O-rings and seals of the LHM system (and vice versa). So the damage was already done and it is only a matter of time for the first symptoms to show up. Symptoms can be a complete failure of the brake system! Actually fresh LHM in a damaged system makes it even worse. Due to our experience then the brakes start seizing in within a week or two.

So if you discover DOT brake fluid in a LHM system (remember: A small amount is enough!) there is no way to avoid this expensive repair!

In very few cases it also happened that LHM was found in an older 2CV's drum brake DOT system. This, of course, has the same result and the car will also need a complete new brake system.