Personally, I wouldn't use the "stops leaks" type of product. The principle of blocking leaks with goo, also tends to clog small necessary passages (e.g. radiator) and may lead to the car running too hot.

From your description of a "musty smell" it sounds like you have standing water, either from a leak or clogged AC drain. A heater core leak will smell "sweet".

Also coolant residue on the windshield is MUCH harder to clean off than normal moisture. It will leave a "greasy" residue.