Last week, we had a contractor come out to give us a quote to replace our sliders and address the issue of corrosion of the aluminum tracks. The contractor was shocked at the degree of erosion. He indicated it is a construction issue caused by a lack of barrier between the concrete foundation and the aluminum tracks of the door jamb. He indicated that normally there is a painted coating or thin plastic barrier between the concrete and the aluminum. If this barrier is breached, the acid in the concrete will eat/erode the aluminum. He indicated it would start slowly and then accelerate (which explains why one door has more damage than the other door track, and why it has become increasingly worse in the past year). He said it will continue to erode until the entire door jamb is gone.