It has taken over twenty years to perfect this process and only in recent years has the success rate reached 99-100%, many units over the years have failed to repair due to numerous reasons that are all basically associated to the condition of the window frame, if there was any problem whatsoever with the frames seals or drainage system the process would fail. Since the introduction of the Anti-Fog Coating and Spacer Bar Sealer 100% success rates are achievable.