The portafilter or filter handles of your espresso machine fit into the group and are sealed by way of a rubber gasket. After a period of time the gaskets can become hard and brittle and will not seal well. If you notice that some water is leaking around the espresso machine group where the filter resides, it is time for gasket replacement. The gaskets need to be replaced on a quarterly schedule, and if you decide to operate on a longer schedule you may find you need to chisel them out. Gaskets not maintained, are very difficult to remove as well. The rubber has a tendency to carbonize and turn very hard.