2001 Jeep Laredo Bluish greasy film on inside of windshield

For about 2 months I've had a recurring film on the inside of the windshield. It's greasy, looks like the window is just fogged up but it's more than that. It smears with your finger like it's greasy, but doesn't feel "wet". It's hard to clean off, and will return. Seems to come from the heater. Looks almost like a window of a heavy smoker, but I don't smoke. I believe it's comiing from the heater or AC. May be anti-freeze? I did have to add Anit-freeze twice this year to top off when light came on. Never had to do that before. But it will take months and months for the light to come back on. No leak on ground etc. Haven't added A.F. In about 3 months or so. Any idea what it might be and what to try. I've never had the radiator flushed, should I try that?