I am trying to figure out if the electric fuel pump in my 1973 Mercedes 450SEL is or is not working. Anyone whose had any experience with these I'd appreciate your input.

The pump is a simple affair, inlet, oulet and two terminal posts. It runs on the bench when I hook up a 12v battery to it. I've taken off the end cap (there is only one) and the little gears, which I asssume move the fuel are bright and shiny, and spin freely. I've replaced the cap with a bit of silicone gasket sealer to insure a tight fit but there seems to be very little suction. Even when I added a tube to the inlet side and forced gas into the hose with a squeeze bottle, to simulate gas coming from the tank, I saw nothing come from the outlet.

Can the suction be measured with a vaccum gauge? What should it be?

There are a lot of MB pumps on eBay, and the prices range from $35 to $400. Is there a good inexpensive alternative?

The car ran okay when I got it (it was free) but that only lasted for about a month before this happened.