I had a leak from the head gasket in my Fiat Punto! Also, when I turned on the heater, it smelled strongly of coolant, indicating that there was obviously a leak somewhere, but I never saw any water on the carpet. Maybe the leak was very small. Regardless, the smell was annoying and made me dizzy! As you can imagine, I had to refill coolant very often! After emptying the bottle into a warm engine (be careful when opening the water cap slowly), the leaks stopped in 5 minutes... the bolt no longer releases any water and the heater stopped smelling... now, only time will tell about its durability... but in the past, I had used a different brand in powder form for another vehicle that had a coolant leak, and it never lost coolant again... don't let mechanics who say to stay away and that everything will get clogged and such influence you... yes, if you have a 30-year-old circuit filled with mud from poor maintenance and repairs, maybe in combination with a certain brand, it could be the cherry on top! Maybe... but personally, I have saved a lot of money in the past and now! Just to have your heater replaced, you won't save 100 euros in labor! And as for solving your problems, they have a party!
EDIT 28/2/23: Still all good! Permanent solution.
EDIT No 2 20/6/24: And we continue!