One of the parts that will need replacement in your aeropress is the rubber seal (also called the plunger). The newer ones are actually made of silicone. When used well, this should last 2 to 3 years. To prevent premature wear and tear of this plunger follow these tips:
1. Expel the puck after you’re done: The puck is acidic and has coffee oils, etc. Although they don’t damage the silicone immediately, prolonged exposure repeatedly can cause it to degrade faster.
2. Disassemble the aeropress after use and store it disassembled: When the plunger is in the aeropress body it is under pressure at the rims. Either push the plunger all the way it to ensure the seal is outside the cylindrical body or keep the plunger and body separate. Constant pressure slowly deforms the seal edges and can cause it to become compressed and leaky. If this happens you can try dipping the seal in hot water for a while and then pressing the seal on a flat surface steadily for a few minutes to get it back in shape.
3. Avoid using the dishwasher: The silicone parts tend to stiffen and crack faster if repeatedly put in the dishwasher. These are not immediate changes and may be seen after several months. The Aeropress FAQs mentions that you can put it in a dishwasher once in a while.
4. Completely dry it if possible: Hard water stains on the edges can cause problems in the long run. Blot it dry rather than rubbing it dry to prevent scratching.
5. Avoid scrubbing with anything that could be abrasive. Tiny scratches can result in a lot of problems. Use your fingers to rub it when cleaning with soap and water.
6. Ensure the plunger is fitted well when preparing your coffee: This ensures that fine coffee grinds do not seep past the edges of the plunger which will cause scratches and may even cause distortion of the edges.
7. Remove the plunger and clean once in a while: This ensures the plunger is completely clean and does not smell with accumulated dirt or oils. I’m not sure if this will lengthen the life of the plunger though.
If your plunger seal is warped or leaky and needs changing, you can buy a new one online. However in some countries these are expensive and not easy to get. So take care of the plunger and let it last many years.