Common question, not so common answer.
First- understand that a windshield does have buildup, everything from bug guts, acid rain, crappy wipers, or old ones, to road grime and oil will "etch" the glass permanently (I'm using ETCH very loosely here)
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That Stoners stuff can act like RAIN-X and leave a coating itself. On the inside thats fine, but the outside it's a danger. I recently posted about a recc. for an antifreeze type washer fluid....Mine freeze ALOT... Someone recc RAIN X washer fluid ..... It's been on a few weeks, only snowed and/or rained a few times, but nearly every time I'm blinded... yes, wipers off or on. ridiculously dangerous!
I read the fine print about "Rain X coating ..." and I'm now ready to slap a windshield on my truck or again, at least try DIRTEX. (I still have a hookup for windsheilds..36$, so yes, it's worth it....)
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Now, for your question, Find DIRTEX glass cleaner. It can only help. We stocked it at our glass shop for many years with fantastic results. Leaves no residue in or out, and its ammonia fortified. DO NOT SATURATE the glass, use some elbow grease.
Good Luck!
MGJ