FerroFluid aging

Thank you for the link, however, that is the one tweeter in the 800 range that is not the same.

Even the link to the 801 s2  doesn't specify FerroFluid or not.  But after seeing it in the 1,25" tweeter I would "assume" it is in the 1" also.

https://www.stereophile.com/content/bw-matrix-801-series-2-loudspeaker-specifications

It's easy to tell if you disassemble the tweeter.  The coil will be crusted over with it and need to be cleaned.

Page 1 section 2, last line on "the drive units" paragraph... It says they are ferrofluid cooled:

http://www.troelsgravesen.dk/BW-802s3/802s3-manual.pdf 

Can the tweeter on the 802 s3 be disassembled?

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.