Try Bon Ami kitchen cleanser.  That is a brand name make sure to use
this brand.  It is safe fiberglass.  Just make sure you plan to wash the
car because it leaves a white powder behind.  I have heard this tip on a
few TV car shows and have used it for years.  The wiper companies use it
before they test wipers.

Adam Oldham wrote:

> I've got a black 89 GTI that has bad water spots on it everywhere.
> The bumpers, windows, paint, rubber, everywhere.  These spots don't
> wash out.  I've had some luck waxing them off the paint, but it took
> me 2 hours to was  the roof of the car with success.  I'm more
> concerned about getting the spots off the windows.  I've tried
> Vinegar, Castrol Superclean, window cleaner,  nothing works.  Can
> someone please offer some sort of advive?
>
> thanks in advance
>
> adam
>
> oldhamanorthstate