Allison tweeters - do they last a lifetime?

[Guest abobotek]

I recently bought a pair of Allison 110 speakers with tweeters manufactured in the 1980s. Unfortuntely, both tweeters were

fried with one shorted and the other open. I gently dissected one of the tweeters partly out of curiosity, and also partly to investigate the possibility of repair.

The finding was distressing: the ferrofluid had dried up!

This may help explain why the tweeter fried: it can easily overheat without the conductive cooling facilitated by the ferrofluid. Loss of ferrofluid also changes the sound, as its damping action is gone.

I read up on ferrofluids and found that they generally are a fine iron oxide powder suspended in oil or water, with a surfactant added to prevent clumping of the oxide. Apparently the surfactant eventually

breaks down, allowing the oxide to clump and the liquid to drain.

So the questions: does anyone know what ferrofluid Allison used and/or how long it lasts? Can overheating the tweeters harm the fluid? Has anyone else had this experience?

I own a dozen good Allison tweeters from the original Allison series through AL 110. They seem fine 30 years later, but I never overdrive

them to the point that they'd smoke (even if the fluid were gone).

series. I've always assumed that they'll last a lifetime. But ...