Looking at the clevis arrangement in the diagram, the part the OP found laying on the ground ... I do not see how you lose that off the tractor. It is fastened securely with pin and cotter key at one end isn't it? If the turnbuckle is still missing and maybe rotated and got loose and fell off ... then the user has to be paying little or no attention to his hitched implements and connections between uses (!) Don't you look at and check your attach points and 3pt area when you start to use it ? No less often than every few times you use it (before or after the operation...) ?? Seriously folks don't most of us do that ?