The building, on the National Register of Historic Places, is 100 years old this year, although the church was organized in 1883.
The windows, I'm afraid, are badly in need of fresh paint.
I'm at a loss to explain the deterioration of the lead. It's not a simple matter of being exposed to the elements. Since the damage is around the solder joints, I suspect that an acid flux was used when the windows were built and was never adequately washed off.