I recently acquired a buick station wagon that began life in Michigan. I think the glass has become spotted with salt and road grime. I have used vinegar, light auto polishing compound and just about every spray-on cleaner I can find with little luck. I read one reply re: spots on a boat's glass and polishing as being the only relief and that might not be 100%. I'll buy a new windshild but don't wanna' pop for new windows. Any advice? tx in advance.