Some of my pneumatics parts, mostly pistons, have seals which no longer prevent the air from escaping completely. On some parts they are unreliable and on others they are not working at all.
Why do those parts become leaky, how can I minimize the risk of it happening with maintenance and/or proper storage, and is there any way to repair already leaky parts?
Zhaph suggested disassembling the piston and replacing the seal with an o-ring, however the seal in question was not a simple o-ring and getting a replacement is properly difficult:

- Top piece locking everything together
- Top rubber seal, with a bit particular shape
- Bottom rubber seal, which is just a wide rubber ring
- A plastic spacer between the two rubber seals
While the top piece appears to be safe to remove, the bottom rubber seal easily gets damaged when you try to force it off the piston. The amount of pressure it could retain after forcing if off a couple a times became limited.