GLC brake fluid consistently low

I've seen similar behavior in my GLC, but mine has a petrol engine. The low brake fluid warning light and strange pedal feel are red flags. It could be worn pads triggering the low fluid level sensor because of increased caliper piston extension. Have you performed a brake inspection recently? Has the system been bled?

I have not had a brake inspection recently, and the system has not been bled since I bought the car. Are you saying worn brake pads could be the primary cause of the fluid level issue?

That is my suspicion. Reduced pad thickness requires more fluid in the caliper to maintain braking force. I would recommend consulting a qualified technician for a comprehensive brake inspection before the problem gets worse. Hopefully they can identify the root cause.

Following your recommendation, I had a brake inspection performed. As suspected, worn brakes were indeed the cause, precipitating the low brake fluid level and pedal feedback. The repair, including new pads and rotors, was 480€ Thank you for your assistance.