I think if the heater core was leaking to the point it needed replacing, you would see a drop in the coolant level, in addition to sensing the sweet smell. I sure wouldn't pull the dash based on my WAG. If the level is fine, maybe just keep cleaning the windows and try to park in the shade, if not a garage.

The best thing I've found for windows is paper towels and glass cleaner, followed by a microfiber cloth with a tiny amount of cleaner. Newspaper also works great, especially for sap on the outside, but I can't stand the feel of it. Like rubbing styrofoam together.

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2002 E320 4-Matic
2008 Subaru Outback
2009 Subaru Forester