Vintage and Classic Games & Toys

i have a mobile detailing company and i have hired the best of the best to ensure people or more than happy with there car, my only problem is windows. i have found that auto windo cleaner works on everything but windows. i still get water spots. i'm not sure but i think its hard water. i have tried regular window cleaner, auto window cleaner, rubbing alcohol, degreaser sprayed on a rag, viniger, and a few variations of some of these things deluted. i hear that steal wool will do it but it only makes sense to me that even fine steel wool will scratch the windows at least a little, and when dealing with $100,000 cars i dont want that mistake to happen. please help (yea, i know, if they were "the best of the best" then i would have this problem right? well, there the best in certain things, one at interior, one at wheels and tires, and ones and washing and waxing and clay bar, nobody for the windows)