1988 240 DL normally aspirated with about 300k miles. Since I've owned the car, I've only used a torque wrench to make the final tightening on all wheel lug nuts and use anti-seize.

I noticed that one front wheel lug nut will not torque to spec on several occasions. Switching lug nuts doesn't make a difference and the lug nut that won't torque on that stud torques just fine on other studs. The outside of the lug nuts are not stripped.

Now I'm noticing that there's a fine metal ring between the lug nut and base/stud, making me wonder if the lug nut is getting damaged.

I don't notice any new problems with the steering given my inability to torque that lug nut to spec.

However, out of abundance of caution, I switched out the wheel hubs with a good hub. The lug nut stud in question is off-car. Examining the threads doesn't show me any problems, except for another thin metal ring, which was not there last time I tried to torque it.

I've never had this problem with a lug nut stud. The hub is otherwise perfectly fine and I'd like to have the hub in service. What's going on and would a die fix the failure to torque to spec issue?

Thanks