Anybody know how to clear a windshield that has scuff marks on it?

What it looks like, is as if someone turned on the wipers when the glass was dry, and let it run for a couple of hours. It's not visible from the outside of the car, but when you're inside looking out, it's noticeable, especially at night with oncoming cars' lights making it more annoying than anything else.

I tried using PlastX, which worked really well in cleaning up the headlight covers, but did nothing for the windshield.

Any ideas?

Thanks in advance for any, and all, replies.

Wes.