have an olds 1998 cutlass which seems to be getting film on front windshield. was told heater core was shot but flushed out and is working fine as heat comes on quickly. let car idle without def on and a film starts to form but mostly goes away but leaves small film behind. dont know if anyone ever had this issue before..

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Does the fogging or film go away when you use Defrost mode, enabling the AC dryer to remove the humidity? Is this a sticky type of residue on glass or just fogging up?
I wonder if the drain tube is clear and allowing water to drain properly?
Is there any sweet smell like antifreeze present?

Just a light fog haze after def on. Can smell antifreeze only when set to pull air from out side not when on recirculate inside cabin air.

Sounds to me like you have a coolant leak somewhere. Are you having to add coolant regularly?
I think I would want to look under the hood for any coolant leaks & at & around the heater core cover inside, and see/smell... if it is leaking..