if the tweeters sound good it's probably OK. The risks to not replacing the ferrofluid on time is audible but also the risk to the voice coil. The gunk may add physical friction and therefore heat the voice coil.
Ferrofluid
Hey guys. So I have been texting someone from Germany I met online as he also has a pair of B&W 800 Matrix speakers. He mentioned that he treats his tweeters every so many years with Ferro fluid. It was kinda hard to actually text about it online with someone I just met from another county. I did google it and looked on utube for some videos and there are some. It’s seems it should be done about every 10 years or so. And u actually have to take the tweeter out of the cabinet disassemble / remove the voice coil clean out the old Ferro fluid and add new Ferro fluid. It’s seems to be some kind of a magnetic liquid used in speakers especially tweeters for better clearer sound, highs, voices etc. It really looks like a job for the experienced in rebuilding speakers. Has anyone heard of this or had it done ? I’d really love to know from folks who had experience with this. My speakers are from the 90s and even though they still sound phenomenal I’d really like to know more about this. I do plan on keeping my speakers for the long term. Thanks to all in advance.