What have you observed that leads you to the conclusion the windows are defective rather than the installation?

You might have better luck dealing with the person who installed the windows. Leaking is rarely caused by the window, but is usually improper installation. Flashing and the method of installation is critical. Think about it. What is more likely; that water leaks through a well built and clad window assembly, or around the assembly through improperly flashed framing and siding. Installation in brick facade (if this applies) is even more difficult. Leaking around the window is not the window manufacturer’s liability.

The celestory windows are more difficult to install and flash. I have at least 10 of these windows throughout the house that have had no problems since 1991. By having a competent installer check the windows, you will either learn that they were installed wrong, or have an expert that can provide you with a report that the window is in fact defective.