Corsa Brake Fluid Loss

That sounds like an issue I had with my old Renault Megane: low brake fluid and a spongy pedal. It turned out to be worn brakes. The system has to work harder, and the fluid level drops as the pads wear down. Have you checked your brake pad thickness?

That's interesting. I hadn't considered worn brakes. I will inspect them. But how would worn brakes alone cause the brake fluid level to drop?

Think of it like a piston. As the brake pads wear, the pistons in the calipers extend further to maintain contact with the rotor. This needs more fluid from the reservoir. Eventually, the fluid level drops in the master cylinder reservoir. If the pads are worn, get it checked professionally to be safe. There could be other brake system issues.

Thanks for the explanation! I took the car to the workshop, and the brake pads were worn. Replacing them and flushing the fluid fixed the problem. The repair cost 480€. I appreciate the help!