Disclaimer: Links on this page pointing
to Amazon, eBay and other sites may include affiliate code. If you click them and
make a purchase, we may earn a small commission.
If your sense of smell works and you are not noticing the sweet smell of coolant, then I'd suspect that the film on the windshield is due to out-gassing of the interior plastics rather than a leaking heater core. Keep an eye on the coolant level just to be sure, but I wouldn't get too excited about it being a heater core yet.