I finally picked up a Redfield 75 to go with my 513T. It is a fixer upper and I've taken care of everything except I need a detent spring and ball for the windage knob. I'm fairly certain I can find a ball, but that tiny spring has been a challenge so far. Does anyone have a source for original springs and balls or aftermarket replacement option that will work? Doesn't need to be original stuff, just needs to work.