I've had this issue on all my cars - the inside of the windscreen becomes 'streaky', especially in direct sunlight. Right pain trying to drive when you can barely see if driving into the sun. Plus it makes the windscreen fog up in rainy weather.
Have tried a few different glass cleaners but find the results are mixed at best. Autoglym glass polishe seems quite good on the outside at least but it's too dusty. Other spray cleaners are largely the same result for me. I usually spray it on, spread about with a microfibre then turn the cloth over and buff off to what usually looks like a good shine. Until I drive it in the low evening sun and can't see where I'm going.
Any tips/suggestions for products, ways to apply it, etc?