Hi Steve - thanks for your reply; I met with my mechanic this morning to make sure I had a clear understanding of the problem. He says I have a new cold enrichment thermostat, and that the problem is that I need a new housing for it. That is the piece that accepts the connections to the hoses an filter. This is the piece he says that Bosch doesn't sell separately, and therefore I need a pump rebuild.
I will try your test tonight when I get home, and let you know. In the meantime, do you know how/where I can get just the housing for the thermostat?