Hi, over the weeks I have got white marks appearing on my windscreen. They are mainly in the centre and in certain light they get in the way of my vision.I have looked online for advice and have tried vinegar,washing up liquid,wire wool,and lemon juice.Nothing seems to work. The screen is smooth and it don't feel like a build up of anything. It seems imbedded in the glass.It looks like frost on the glass but it is dry.Has anyone else had this on their windscreen? How am I meant to get rid of it? Can anyone help?