Fuel Accumulator Connection
Thanks for the reply. I just found not 10 minutes before this reply a diagram which shows that the vent line does connect back to the fuel supply line. It did not appear so under the car, but I'm sure that is the case.
A Bosch diognostic manual said to check the vent line. But Mercedes connected that vent line into the fuel supply, so the test is invalid.
Oh well, back to the drawing board. I'll probably pull it out to check it, since I don't yet have a Bosch-compatible fuel pressure gauge.