The diaphragms in the Perry pumps dry out. They need to vibrate at whatever designed frequency and amplitude to work properly. I bought an older Perry pump which didn't work; I called them up and was told 'there's no way that pump can still be good' due to the age of the diaphragm and subsequent degradation. So it is a good idea to keep them moist and not run them dry.

I found it easier to switch to stainless bearings and forget about maintenance, whether it works or not.