Ferrofluid

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.

@timlub Thats exactly what Bill said at Millersound about it thickening as it ages and will harden overtime. Do u also build crossovers. ? If u do and or know about crossovers I would love your professional opinion on the crossovers from a maker on eBay as I mentioned a few posts up. You can look them up on EBay if u have it. Just search for B&W 800 Matrix crossovers. Thank you and I appreciate it. 

@tattooedtrackman     Yes,  I do design, build, mod and repair crossovers.  I know what I'm doing and want you to please take to heart what I tell you  here. Your speakers crossovers are well thought, complicated expensive. When I build,  Each woofer, tweeter mid, midbass and each crossover part is hand measured and matched for accuracy. If you want someone to replace caps and resistors, fine, upgraded parts will be audible, but understand, 1 person may say Wow, what a shocking improvement and another may say, well, I can tell its done, but it wasn't much different.  You can spend a ton and not hear alot of difference. With that said, when you replace inductor coils,  you are changing the line impedance sometimes over an ohm on a single part.  If you take off a 3mh ferite core, it may have a resistance of .8 ohms, when you change to a 3mh air core, it could be more than double that.  So you think you have a crossover frequency of say 3000hz, but because you changed the line impedance to that part, you may now be at 2800 or 3200.  On top of that, when I build, I build to have phase and time alignment, when you change parts without a proper plan, you throw that right out the window.  If you want to replace resistors and a few caps, I'm happy to pull schematics and tell you which to change and good idea of what to buy, but unless you are very highly qualified at speaker design, do not change the inductors.  It is alot of work to get this right and it is easy to blow by someone that can solder, but really doesn't know what they are doing,  So EBAY, for me, especially on such a nice speaker, That is a big NO WAY.  

@timlub   Tim. Thank you for your detailed reply. I really appreciate it. I want to say first if all that I would not even think of doing this if I didn’t have someone to install and solder the crossovers in for me. When I first bought my ARC REF 750s and was playing them the first few hours I had a tube arc and it took out a resistor. I called up my ARC dealer here in NJ and he hooked me up with an awesome Technician. I ordered what I need from ARC and when the parts arrived he came to my home and installed and soldered everything and also checked both amps out and gave them a clean bill of health. And said that they are in excellent condition. So when I told him and showed him and had him read about those ( supposedly) upgraded (better sounding 🤷‍♂️) crossovers on EBay he said that they sounded good. And that he would have no problem replacing and soldering them in at my home.Now mind you and I know he does not build crossovers or maybe he does not know much about building crossovers other than how to install and solder them. So he is just probably also going by what he read about them from what I sent him. Ok. Now I have some questions and opinions from u Tim. Knowing that my speakers are from the 90s and since I had them now about 8 yrs now and really never had a problem with them. Would u think I would need to change or replace the caps and all that is involved in the cross overs ? Wouldn’t that be like an amp dating back to the 90s ? Changing upgrading the caps and resistors etc ? Also what I did want to mention is the only issue I do have with my speakers is the highs coming from the tweeters being too bright along with the voice. Now it’s not all the recordings but many. My question is if I do change and upgrade the crossovers can something be done about that with the crossovers from the tweeters ? Now let me also say that I only listen to digital. I also have a ARC Ref 6 that I bought brand new a few years ago and only put on 600 hrs. I did just have gotten it upgraded from ARC to the Ref 6 SE. and have it now for about 2 months. All my tubes in my amps and pre amp have about 700 hrs on them so I know it’s not from the tubes. But it’s really that brightens and some recordings are too bright IMO. Other than that the speakers sound phenomenal. Especially the powerful bass. And I really thought u was going to loose ALOT of that when I replaced my Krell FPB 600 which are known for thunderous bass with B&W s. But it’s definitely not the case. I did loose some but definitely made it up for all the other quality’s with the ARC 750s. Now I also wanted to ask you IF I did want to upgrade all my 8 crossovers can u possibly make them for me with your expertise and knowledge? 

@timlub Also forgot to tell u I also have and am using 2 Krell B&W BAFs. ( Bass alignment filters for my 800 Matrix.u can also see my system and all the components and cables etc etc from my profile.