When do you need to get a new diaphragm?

When well used: When it is a couple years old, looks weathered, yellow or cracking. If it has dried up in a drawer for a couple years or if you left in your car in phoenix today(116 degrees).

Old and "holy": If a diaphragm is more than 5 to 7 years old, the rubber component tends to deteriorate, making for a "blessed diaphragm" which means it is 'holy". If a hole is seen at any time when inspected post use, change it immediately- as they are cheaper than a undesired pregnancy.