The capacitors are probably still fine in your speakers. Capacitors would be easy to replace, and someone may so do to use better caps to improve the sound or preempt future concerns about them going bad. You can easily do the work yourself, so that is another factor in favor of replacement. But, the fact that a particular cap is a current favorite does not guarantee that you will like a particular change; it really is a matter of matching your taste and particular system. If you go the route of changing caps, keep the old ones in case you don't like the replacements.
I have no experience with ferrofluids so I don't know what it takes to clean out the old fluid and replace it with new fluid. If it is not something you can do on your own, you will have to remove the tweeter to send it to a competent service technician. You do not want to ship your whole speaker. That would not only be expensive, it will be quite risky in terms of damage.