It’s easy enough to replace FF if you can open the tweeters up. Did it with my Seas H400 tweeters a couple of years ago, and was surprised that it made an audible improvement once replaced.
Once the voice coil is separated from the magnet, take a piece of index card or folded paper and scrape out the residue from the magnet gap. Refill it with fresh ferrofluid about 3/4 up. It’s useful to have a syringe or squeeze bottle with a fine fill tube for injecting it into the gap. It’s not rocket science, and there are plenty of pics and vids on Google.