if the film is on the inside of the windshield, it's likely a pinhole leak in the heater core. Losing coolant? Almost certainly.

POTATO!?!?

Well, I heard once that jewelers rouge and a polishing wheel on a drill will buff out light scratches, and also that TOOTHPASTE will work too (plain old CREST). Needless to say I looked like an idiot smearing jewelers rouge and then toothpaste on my windshield and buffing with that wheel to get ....no results. Get a new windshield if it bothers you. Enjoy watching the glass guys replace it, and do something with your kids/grandkids with the time you saved by not doing some half-assed fix to try to save a few bucks.

Seat heater switch: Might be the switch. They sit in a bad spot and get all crudded up with all sorts of dust and grit that settle in that part of the console. If you don't want to buy a new one needlessly swap the one that works with the one that doesn't. If it still don't work than I would check the thermostat wiring and connections.

It's more likely the wire to the thermostat has come loose. I think there's a piece on repair in the FAQ's.

As for the windshield, it may be that after 13+ years that the wipers have left their mark. I could never really clean up my windshield, so I replaced it. It did have a lot of little pits from sand and sharp gravel used on snowy Maine road, so it wasn't just that "film" look where the wipers overlap that led me to replacment.

I believe a potato cut in half will do an excellent job of cleaning the oily film off a windscreen (I have never actually tried it, though). I can't help with the other question (I drive a 244- 740 is a dream at the moment!)