Over the years, these things will continue to work but will lose pressure little by little. Once they begin to leak, you can feel and smell the gas in the oil.
Guess I misunderstood your original post. I thought you were saying diaphragm failures were common on K and Magnum engines often causing major engine damage. Now I am confused. How often have you personally experienced diaphragm failures on a Magnum engine? Did it actually leak enough to thin the oil and damage the engine or are you simply saying that is a possibility if the operator isn't vigilant?