I dissassembled the slide easily enough and when I went to put it back together, I cannot get the endcap back on. I can slide it over the firing pin plastic bushing in the center of slide, but cannot get it over the extractor spring. I can't seem to push the extractor spring in far enough. I put the black plastic extracor in the side of the slide first, but the white end plug on the spring will not compress enough. Any suggestions?