Ferrofluid

I have changed the ferrofluid in my tweeters.  The ease or difficulty in doing so depends entirely on how hard or easy it is to dissemble the tweeters.  It turns out in my case it was easy to dissemble to tweeter to be able to get to the channel where you wipe out what's left of the old ferrofluid and add the new.

Personally, with nicer speakers like yours I would just send the tweeters to Millersound and have him do the work.  I'm sure it would be quick turnaround (guessing days) and very reasonable and Bill is great to deal with.

Millersound Speaker Refoaming, Speaker Reconing and Repair Services

Regarding "ferrofluid", from the net:

"Ferrofluid cools down the speaker coils which are susceptible to extreme heat. Ferrofluid transfers and dissipates the thermal energy produced by the strong vibration of the moving driver. As magnets increase in temperature, they lose some of their power."

Better yet, see if you can talk with B & W about the advisability of updating the crossovers or not. 

There is no set rule regarding how long ferrofluid lasts.  I have read 10-15 years is typical.

Chances are your ferrofluid is still basically still ok and you will hear little or no difference after having it changed, but who knows.  My speakers were also built in the 90's, and I think it is wise to change the ferrofluid to ensure no damage.

About the crossovers, I will leave it to the experts here to recommend whether or not to update them if they still sound great.  The question is if crossovers with high quality parts like your (and my) speakers last longer than those with more generic parts?  A quality repair guy once told me he thought they do.

@tattooedtrackman  I will defer to those with more experience.  But if it was me and I did not notice anything that sounds wrong, as in your case, I wouldn't even think one thought of messing with my crossovers.

I would just sit back and enjoy your beautiful system.