Chiefs, Gurus,

I have this vintage Galant with a 4G63 Carbureted SOHC engine. I noticed lately that the water from the reservoir lowers everyday (but minimal only) and that a somewhat sticky substance sticks along the container walls (minimal also). Also, while the engine is on idle, i tried opening the radiator cap and I noticed a minimal whitish smoke or mist coming out of it. Before, everything is normal. I consistently replace my water with a distilled one and also add a coolant. Can you give me the possible causes of the mentioned concerns? I don't want to think that my head gasket is busted (it'll surely mean money! ) One more thing chiefs, my radiator water smells a bit gasoline!

Thank you so much for your reply and suggestions! More power!