Tweeter life

mozartfan, AFAIK ferrofluid in tweeters is used for damping and cooling.  It has nothing to do with type of the magnet.  Neodymium magnet tweeter might be designed with or without ferrofluid.

The fact that magnets "lose some power over time" speaks against replacing them, because other speaker magnets (midrange and woofers) lose some power as well.  I would rather lose some efficiency than risk unbalanced sound.

Why to replace tweeters and not the woofers? Dry ferrofluid can be replaced. Large midrange drivers in my speakers also have ferrofluid, plus unique design - not replaceable. Replacing tweeter is not an easy task, unless you reinstall exactly the same. In addition to sensitivity, that you might have to measure somehow, you need to match resistance and inductance of the coil. Also dispersion characteristic might be different. My 11 year old tweeters are short horn by unknown manufacturer while speaker manufacturer bankrupted. There is no provision to replace ferrofluid - would have to unglue membrane. I found similar short horn tweeter (Morel), but would have to measure and compare inductance and sensitivity. Current speaker has no markings on the posts. How to determine polarity of the tweeter? (some speakers have tweeters wired in opposite phase). Would new speaker improve sound or make it worse? My brother’s Cabasse speakers are over 20 years old and tweeters still
work fine. Perhaps "if ain’t broke don’t fix it", unless you have "Gardener’s Syndrome" (constant trimming and repotting).