It is really hard. I bust my rear trying to pump enough for my baby and my DH (who stays home) is respectful of how hard it is for me to pump, but a little goes to waste now and then and I totally want to cry!! It's not easy pumping all the time!!
Pump parts do get old. Have you already tried replacing your membranes? Those seem to wear out quickly on Medela pumps.
I agree, you need to have a firm talk with your DCP. Like, this is what you're going to do from now on. Give them small bottles already filled with the portions you want them to use (3-4 oz). If he still seems hungry after a bottle, maybe they could offer yogurt (yogurt is one dairy product that's allowed before one year)? I also agree that 16 oz is not a realistic amount to pump in a day - I am a great pumper and I generally bring home 12-14 oz for my 8-9 hour day.
If you're driving a lot, have you tried pumping while on the road? You get everything set up under a nursing cover or poncho (fasten your seatbelt before you put the horns on) and turn on the pump. Then drive. I find it to be a relatively low stress way to get an extra session in.
Just some ideas here. I know it's really tough, but it's worth it. You can do it!!! Hang in there.