Joy, I'll be interested in the other replies. My own experience is that sometimes the piston/cylinder becoming "sticky" and they don't glide smoothly anymore; the resulting friction stresses the pump motor. Sometimes this can be remedied by oiling the inside of the cylinder with oil (I use vegetable), and sometimes it is the white gasket on the piston that must be replaced; other times, I must completely replace the cylinder. Why this occasionally happens, I'm not sure; I haven't tracked whether the moms have done anything unusual with the pieces, ie boiled them, etc. Looking forward to hearing more! -Lisa Marasco, BA, LLLL, IBCLC