I think it was in the late 1970's that GE's Silicone Plastics division came out with a radical new liquid, sold in something like a 6 ounce bottle, that treated windshields and made the rain just run right off. Rain-X didn't exist then. Then federal child safety laws required child-proof caps on everything, and GE pulled the stuff off the market because, literally, it was so slippery that no child-proof container could contain it without leaking!

The GE stuff was great. Rain-X is all well and good, but it eats "plain" rubber wiper inserts that some manufacturers use. (A $3 insert does the same job as a $30 wiper arm blade, it just isn't as profitable.) So personally I gave up on Rain-X a long time ago, I don't want to experiment with it. If I really want to get the glass clean, I use the aerosol version of "Invisible Glass". Aerosol, not pump spray, because anything (including Windex) that is exposed to oxygen in the bottle eventually goes off, and the sealed spray can can't lose volatiles that way.

I don't know what's in the stuff, but it does a damn fine job. Even better than a new bottle of Windex, fwiw.

One solution to rid glass surface smearing is to remove all the accumulated stuff/junk/acid rain etching off the glass. OTC glass surface cleaner will not work. Treat the glass like a painted surface by doing something similar to a 'paint correction' on the finish and use the least aggressive polish (Mequiars?) and buff the glass surface clean with a random orbital buffer. In the past on very chemically dirty glass some use a 0000 grade steel wool with a diluted metal polish with excellent results.

I clean with invisible glass, clay bar the windshield, rainX, and maintain with invisible glass. Clay bar really helps with water beading and doing a thorough clean.

I use bronze wool. Less likely to scratch. Available at marine supply shops and some marinas.

Best to use bronze wool. available at most marinas and boat supply shops.
less risk of scratching the glass.

If you really want to "chew" on a windshield, 3M's ScotchBrite pads are available in something like 8-10 grades from around 200 to 2000 grit. (I owuldn't use anythiung coarser than their non-scratch kitchen pads on a windshield.) And there's the inexpensive Mr. Clean Magic Eraser, which is actually a 3000 grit melamine foam sponge designed to turn to dust and be consumed as it is used. That's the same thing as 3M's 300-grit Finesse polishing compound, which leaves a mirror finish on things, and the same as clay bars, which are just 3000-grit adhesive mixed into a clay carrier.

But I've never met bugs or goo of any kind that wouldn't come off with plain ammonia and some elbow grease. No residue left behind after a simple rinse. Ammonia is what is used to strip industrial floor waxes, and spray-on car wash waxes are the #1 cause of streaky windshields.

Hi!! I agree, but the steel wool that bpp suggested is much harder than the bronze wool.

Ms.
 

I have had REALLY BAD marks on my glass, that are more visible when sun hits from the front or it rains, or there is condensation... I thought it had to do with a different carwash I used, until a friend with same car (Q3) told me she had the same. I also tried every household cleaner for glass until someone told me to use compound (for car scratches) on glass and rub hard, in circles (muscle in), and later clean with soapy water. It worked!
See pictures of before.
https://cimg7.ibsrv.net/gimg/www.aud...5b165ae1c.jpeg
Sorry about sideways, don't know how to fix
https://cimg9.ibsrv.net/gimg/www.aud...a9a2c8785.jpeg

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In regards to streaky/stained glass, no glass cleaner will alleviate the issue. You will need a glass polish or an abrasive automotive paint polish and machine apply it to remove said issues. They also make "water spot" remover and might be able to fix this issue as well.