Hi Guys,
In regards to stains on glass, the first thing to work out is if it is a deposit sitting on the surface of the glass or has it etched into the glass. Generally if it is a surface deposit it can be removed quite easily with the right products.
One recommendation no has added is to use a glass polish designed for Automotive Glass.
We have a few options available on the Waxit Online Store. You can try having a look here.
Firstly I would try white vinegar on a sponge, this seams to break down the alkaline in the mineral deposits on the glass, Soak a few paper towels in vinegar then leave them on the windscreen for 5-10min. Use another vinegar soaked paper towel to remove now dried paper towel and check to see if this has worked for you.