I have noted a clunk from the top of the strut where the top nut holds a dished rubber bushing to the strut bearing. I have been able to tighten this a few turns by hand with considerable effort. The clunk remains, although perhaps slightly less noticeable. How is it possible to tighten this nut further? What is the factory torque spec for this nut?

Also, what is the dished bushing called? I have not seen it offered at sites such as IPD. Is this a commonly replaced part on a 12 year old car? The rubber seems a bit hard, but very much intact. Is it adviseable to add a washer under the nut to facilitate further tightening?

Thanks in advance for any help you can offer.