I whole heartedly agree with tomh. I have had Anderson windows, self installed, for close to twenty years with absolutely no problems. Even in driving rains! If the flashing and installation is not done properly, ANY BRAND of window has the potential to leak. Without seeing them, but from what you have said, I believe you have “faulty” installation. I would have an experienced “home inspector” examine the installation. Then document, document, document and SUE for damages in “Small Claims” court. You do not need an attorney and filing fees are generally around $25.00 to $35.00 Generally you can recover up to $5,000.00. Depending upon the state you live in.