Dirty Windshield Problem

[chips-b-gone]

I have recentlyaquired a contract doing headlight restoration on our city police crusiers. The Captain I am working with has a car that he has stated that whatever he does to try to clean the windshield on his car is still looks dirty. No rock chips or cracks of any kind so I have ruled out internal contamination. What can I try to get his windshield clean??? Maybe claying the glass or using a final polish with my porter cable moving at a moterate speed? Any input would be gratly appreciated.

[imported_themightytimmah]

Glass polish via PC on the outside, via hand on the inside. Zaino makes a good one.