For those that are not having good results after assembling their pump, make sure that the front and rear plates (i.e., the plate at the front near the shaft seal and the rear case) are assembled correctly with respect to their rotation about the shaft. The rear case is fixed and can only go on one way, but the front plate can be incorrectly installed.
The pin that the internals rotate about (at the bottom of the pump) must fit into the front plate (there is a small hole) as well as the rear case. You can see this hole in the pictures at the beginning of this thread. It is possible to assemble the pump without lining it up, but it requires a lot of force since the pin sticks out further and deforms the rear case. (Don't ask how I know.....)
At any rate, the grooves that pass through each plate should be 180 degrees from each other. That way the fluid can come through the back (I think) and go out through the front. If you put them where they line up with each other (incorrect), the pump won’t deliver any pressure.
I tried to post some pictures with arrows to make this more clear, but I wasn’t smart enough to do it without authority to post attachments.