[dutchman1]

You should be able to use a torque wrench. After you get the nut tight with your box end you should be able to remove the allen key and torque it without it spinning in place. Also disconnect that endlink altogether and move both the ball joints on the end through their full range of motion and make sure they're not binding. If it binds in the right spot it can act as a wrench on the stud and loosen it up.

I've always torqued mine with a torque wrench, and through over 300 autocross runs and 25k street miles have yet to have one come loose. If you'd done the above and it still comes loose, a little red loctite will do wonders. Just don't put so much on there that it drips into the endlink joint.