I don't want to bother you with my questions, but my reperture seems endless

So, after yesterday, we're going to have my weakening alternator in about. 2 hours has changed, another problem arises: in my interior it's funny! At first I thought it was gas, others think it's more like coolant! that would also fit the fact that I am on 1000km approx. 250ml of cooling water must be refilled! I wonder, however, is it possible that I lose so much water on the heat exchanger without which my interior is damp or. I have foggy windows? for I have not noticed that yet!
If it's the heat exchanger, I can also change the annoying squeaky fan! Does anyone know what a new fan (motor) and a heat exchanger need to be rolled out in the specialist store? what else do you need for parts?tige heat exchangers seen on eBay, has anyone ever installed them?taugen die what?
Would I be very pleased with a detailed answer!
Greetings Rainer

