A worn button or valve core is the most common cause of air or water flow failing to cease (leak) when the button is released. In such a case, simply replacing the worn button and/or valve core is in order. You will have to remove the old button(s) from your syringe. Buttons are held in many different ways – a quick examination will allow you to determine if they are:
Held in by a retaining pin which runs through the head of the syringe from side to side- very common on most of today’s syringes.
Held in by friction- no other apparent methods of retention.
Threaded- there will be flat sides directly below the “cap” of the button onto which you could put an open-end wrench.
