So after sitting a few years my Listeroid 6/1 Bosch Pump was all gummed up from straight biodiesel left in it. I soaked it overnight in Xylene and it freed it all right up and everything seemed to be moving freely. The first odd thing I noticed was if I screw the drain screw in the back all the way it stopped the rack from moving, so I figured a rubber washer must have been there and disintegrated so I added a rubber washer... Well I was going through all the steps to get air out and all went fine until I got to the last step where I connected the hard injector line. Turning the engine over nothing pumps, no fuel comes out. Now if I remove the top bolt and take out the spring and turn the engine, the small part in there pops up like normal and fuel wells up and overflows, but if i assemble it all then nothing pumps. So Im wondering what happened. Was there more rubber parts in there that disintegrated? It does seem now that the small part (I believe its the delivery valve) in the top that the spring sits on is looser now, it pops up and comes out easy. I never noticed that happening before. Im wondering if that back screw isn't just a drain but it also holds something in place? Any information comments and advice welcome here.