Warped shed door

Double doors on shed. The overlapping door has a gap at the bottom. The door has a tensioner on the top half and bottom half of the door, hinge side to open side at opposite angles. The tensioner at the bottom that I would need to tighten to pull the bottom corner in does not work. It screws apart instead of tightening. Seems the threaded parts are incorrectly threaded. The barrel in the middle will screw from one rod to the other until it come off one rod or the other depending on which way I turn it. So it does not tighten or loosen it just moves.
Anyway do you think I should buy a new tensioner or just install 1/8 inch thick 1x1 angle iron on the opening side of the door to pull the 2x4 straight? There is plenty of room to install the angle iron. Would a correctly working tensioner be better? If I buy a new tensioner can I be assured it will work and not be like the one I have? I am going to check and see if the other tensioner for the top of the door works correctly. Not sure why the bottom one does not.

 

I think what you are calling a tensioner is a turnbuckle. Sure sounds like it was defective from the start. As you say, turning the barrel should pull both ends in or push both ends out depending on which way you turn it. They are inexpensive; I'd probably replace it first and see if that does the trick.