The top hat is suppose to have a D shaped hole that locks to the D shaped strut rod. If the strut rod is turning inside the top hat, then the top hat hole is most likely worn into a round hole.
If this is what is happening, then you REALLY NEED to replace the top hat so it locks the strut slider properly. My old Z had a knocking noise in the front end when I got it. Didn't find the source of the noise until I upgraded the struts. Good thing too, because with that hole being oversized, the strut rod moved enough in the top hat that it wore half way through the rod.
If you can't get the strut rod to lock to the top hat, then there is no way you will be able to torque that nut to the proper torque. If the nut is at all loose and allows the rod any wiggle room, then it could start to wear. That is the only thing holding that whole corner of your suspension to the car.