No glass cleaner puts a dent into the accumulated crusty layer of deposits on my windshield and other windows. Can I buff it out, and with what sort of compound?
It may need to be replaced. I suspect 10 years of dirt and sand hitting the windscreen has scratched and pitted it. You are not likely to be able to buff it out enough to get it really good.
Superficial pits and scratches in glass can be buffed out with a polisher and glass polishing compound, but it is very time-consuming and skilled labor. At today’s glass prices, it is cheaper to replace the glass unless your particular glass is unavailable.
If it is just soiled, you want to use water spot remover. This is a very fine white powder (clay) that you use like scouring powder.
This is quite a job also, so plan on doing your windshield in about four sections on four different days, unless you have really sturdy arms. The good news is that you only have to do it once every decade.
The stuff I use is called “Nothin’s Better” from Watkins of Sacramento. I doubt that this product is available since I bought it 15 years ago (and still have over half the jar left). I have done 4-5 windshields through the years with it. There should be something similar available on auto detailer supply websites.
Try using Brasso metal polish to clean the glass.
Dampen a rag with paint thinner “odorless mineral spirits”.
If you need something stronger try lacquer thinner.
I’ve used Brasso with very fine steel wool, and even a hand held vibrating sander with a very fine synthetic steel wool pad. It works pretty well on shower doors, too.
If your windows are so badly messed up that replacement is a real alternative, then you’ve got nothing to lose by trying something like this.
Do not buff. Too aggressive of a buff can put divots in the glass and can distort your view ( at least I have heard this from seasoned professionals ).
I would try 0000 steel wool.