Do you have moisture in your windows ? This is often caused by broken seals between the two panes of glass as the windows age.
This company provides an excellent method for removing the moisture and delaying complete window replacement for years. We have been using this company at our condominium complex for more than 6 years, treating 75 - 100 windows. Results have been excellent. The operator can be relied upon to make corrections when problems ( very infrequently ) arise.