If I understand, you cleaned out the reservoir, you removed the fabric covered hose from tank to pump and looked through it to know for sure it is not blocked, you also looked at the nipple on the pump that hose connects to to be sure no crud is obstructing that opening, you assembled and filled with fresh Febi or MB hydraulic fluid, you opened that banjo bolt per locry or disconnected high pressure supply hose per me, you ran the engine for 1-2 minutes at about 2500 rpm, and no hydraulic fluid comes out of the pump......we must say that pump is no more, it's deceased, it's expired.

The very last thing I tried before buying a new pump was, on the bench, drip/pour fluid into the outlet side while spinning the pump counterclockwise to see if any junk can be forced out. Air won't do it, use fluid.

Bummer that MBpumps is also no more- I hope I wasn't his last customer

Used pump from Potomac German Auto Frederick MD?