Hi
I think you should try concentrating on the tops of the frames, clean them but don’t over wet them, let them then dry out, then clean them again, once the second clean on the tops of the frames has dried, clean the actual glass, but don’t go right to the top and hit the top frame. This should stop 95% of your spotting. I would also concentrate on your rinsing, you need to rinse the window properly once washed, start from the top and go side to side working your way down (don’t rinse the top of the frame though). Hopefully this will help you. If not, use a window degreaser on your windows first, then wash them.
Another Problem might be the brush you are using, some Viking brushes brake up as they are used and this can cause spotting. Take a look at the end of your brush; if the bristles are split at the end (fuzzy looking) your brush is too soft and not adequate for window cleaning, designed more for fascia board cleaning.
Andrew