Some of those elderly sidepulls didn't stay in adjustment very well, which is probably why someone decided to "fix" them and they didn't get it all put together right, usually the way to fix them is to disassemble them, clean the parts and then reassemble using fresh grease on the parts that interact with each other, except the shoes of course.... You need a couple of parts actually, one is the washer with the notch to fit the spring, and a new bolt, because when a nut with the wrong threads is used, it destroys the threads, you also need the proper nut. I would look for a replacement brake unit and throw that one in the junk box.....