My house is about 100 years old. The seal in the rear is just about gone. I have two door s in the rear and have removed both thresholds to inspect the damage. The problem with starting the replacement job is the logistics of the operation. Under the house in that section there is only about 1.5 feet of clearance. On the exterior, there is a deck with a screened porch that runs about 2/3 of the house. I haven't noticed any major shifting yet, but I am concerned that the longer I wait the more I will have to correct in other areas.