sadie...it's something to do with inner workings that can't be cleaned. www.medela.com
says what that part is.
But really, I think it's probably mostly a CYA thing for Medela since there's a possibility germs -could- be transferred. I think the main concern is probably HIV...and that doesn't live outside the human body for long, right? Sooo...
I think there'd be an issue with sharing a pump while both moms are lactating. Right now, I am the exclusive user of the pump. I'm not pumping and then letting someone else use it that day or even that week, kwim?
And for those of you using a used pump, don't feel gross. Think about it for a second. We have had posts on MDC about breastfeeding babies who are not our own and about breastmilk banks. I don't think either of those things is necessarily icky. Is using a pump you've cleaned the parts of yourself really that "gross"?