One of the great things about slate roofs, is their ability to be repaired, without throwing out the whole assembly. In 2008 Louisville was hit with a major wind storm which caused some gargoyles to fall off the secondary tower on St. Boniface Catholic Church.
The going price for salvage slates was very steep. For visible areas: it is always best to source salvaged slates of the same quarry type so that the weathering matches. Since that was not available in this case, we purchased new slate at a much cheaper rate, and grafted old slates from an area behind the tower that is not visible from anywhere on the ground. This provided a very good match for the visible repair area.