Did a job today where above some french doors there is a partially exposed steel lintel, water seems to have dripped off this (rust markings) and run down the upvc top frame causing a yellow run and then down the glass top to bottom causing a sort of grey/white etching mark, tried cleaning it with one of those white pads but it wont shift it, get it wet and you cant see it but as soon as it dries it's back.
Anyone have any ideas what will shift it.
Thanks