I'm not an expert, but reading the details, makes me wonder if the actual master cylinder is ok. The hydraulic clutch is just a sealed tube filled with fluid, if after all that pumping there is no pressure, but no puddle of fluid somewhere then maybe it is being pushed into the resevoir when you lock the nipple at the slave end. If I'm way off the mark, then apologies, as i'm used to working mine which is just a master, pipe, slave arrangement.