Aged ferro fluid in HF drivers - Possibilities of ways to test?

[Bytemee6666]

I am the owner of a pair of AR90's (purchased new in early 80's) as well as a used pair of AR11's, and in both cases I was reading about the fact that the ferro fluid in the HF drivers ( tweeters) may be aged and affecting performance. I don't know about anybody elses thoughts of testing to determine if they are going bad, but, I did have the idea that a test for a "voice coil rub and buzz" on a HF driver could be done with a Dayton Audio DATS unit. This test first runs a frequency sweep from 20 to 20KHz to check impedance with a bode plot display, then, runs a lower voltage level sweep and compares them, checking for any abnormalities that some kind of mechanical interference might cause and would be more prominently affecting a low level signal than a higher level one that might overcome a mechanical issue, and designates a good/bad grade as a result (you can change the grading parameters prior to testing if desired) What are anybody's thoughts on this, or, has anybody else come up with a testing solution they would like to share?