This is from the Kolbe & Kolbe website, their FAQ section:

•14 - What can I use to clean my vinyl windows?
A few drops of a mild liquid cleaner in a bucket of water is
sufficient. If you have more stubborn build-up, the following
household cleaners work well: Formula 409, Ajax Liquid Cleaner, Murphy
\'s Oil Soap, Lysol Cleaner, Soft Scrub, or vinegar and water. The
following cleaners or types of cleaners should NOT be used on vinyl;
Clorox, Pine Power, Ivory, Grease Relief, Tide Detergent, nail polish
remover (acetone).


If all fails, there is a paste polish that glass companies used....
can't recall the name. About $30 for a 6 oz can. It is used to sand
out small scratches, unusual finger prints, etc. Very fine grit... It
actually sands down the glass to remove whatever. The same stuff lens
polishers use for making/cleaning lenses for things like telescopes,
microscopes, etc., also. Maybe your local glass supplier will sell
you a tablespoon. It doesn't take much, if you only have a few spots
to clean/repair.

Sonny