I bought a pair of Arivas new in 2004.
I still have them and love them.
Especially the fact that they have 3 drivers, and the bass one down near the floor adds a very wide spread of sound.
You can tell how old yours are from this list: https://www.naimaudio.com/serial-numbers
I replaced one of my tweeters that had been damaged - Darran of Class A ordered it from Naim and screwed it in for me.
I don’t recall doing anything on the crossovers.
I think it would be very difficult to get at them as they are sealed box design.
Why do you think they need it? Just on principle that the caps might have dried out - or do they sound off?
Do you have them nicely spiked and levelled on their plinths?
If you have any queries on them you might ask the brilliant Duncan Roberts at Naim.