Extending the antenna may have made the situation worse. It is probably cut to a specific resonant frequency. Extending it would change the antenna's resonant frequency to something other than its design frequency. How did you extend it, anyway?

Any changes in the building, such as large objects that have been moved, structural work? Anything that could be blocking the signals?

Have you had a lightning storm recently? The receiver may have had a component fail, which resulted in reduced sensitivity instead of a complete loss of function, either due to a power spike or just plain old age. Replacing the logic board of buying a whole new GDO would be your two options. At fourteen years of age, a new GDO makes the most sense.