I have a 7 month old and have started back to work part time. The amount I pump has been dropping over time. It is not uncommon for me to get one ounce total per session these days. I have read that pump parts need to be periodically replaced, but how do you know which parts and when they should be replaced? I have the Medella PIS. I bought it new when baby was born. I feel like I have tried everything else, except herbs, that might help (I do compression, massage, drink water, pump during different times of the day, eat oatmeal, etc.) I do not think it is a supply issue because nursing is still going fine.