Benfirst, I am not sure you got this figured out. My 84 30E has the same pump, which stopped working. The issue ended up being dirt stuck in the valves which prevents the vacuum effect it should have when pumping. I took the pump out ... had to crawl into the cockpit locker and be in an awkward position for a while to get the nuts in the back out. And when you put it back on, you need someone to help hold things in place and put in the screws while you hold it in place from underneath.
Once I cleaned it up, I put a filter on the other end of the hose inside the bilge. This was to make sure more dirt does not get sucked in and get it stuck again. Been over a year now and the old pump works just fine.
search this forum for 30E and you will see another thread where I was discussing it a while back.