Wow. I like this guy, he posts good pictures and diagrams and everything!
So I have two questions. At the top of your diagram (as pictured) your o ring is floating (I edited to show this) and also there is this spring portion that I don't see the purpose of. Does the rod slide through the disc? The pressure should be enough to force the disc against the o ring, making a pressure seal. Is the spring just an original part of the soap pump?