Caulking, when exposed to the weather for a number of years, can dry out and chip away. If you don’t re-caulk the outside edge of your sliding patio door track where it meets the cement, rain water will seep in and rot the wood below. As the wood softens, the track sinks about 3/4″, just enough for the door to clear the track above. Then, when you open the 200 lb door, it falls on you! We have seen this more than once. If your patio door track feels a little squishy when you step on it, you might consider a little maintenance before it becomes an issue.