Are the mavic freehubs servicable and if so where will I find some info about assembly and disassembly. If not how best to keep them running freely.

Yes they are servicable, it’s been a while since I did one but I seem to recall undoing the end caps using allen keys in the axle ends. Some have a plain bush for the freehub to run on inside the hub shell, some have a roller bearing that may dump it’s rollers when you pull it apart.It’s simple enough to clean, regrease and re-assemble.
Try the Mavic website for the UK service centre number if you need more info.

dont worry they are very very easy , i did my SL’s at the weekend.

the mavic website has a guide for the dealers but do a search and plenty on people have posted the passwords.

Mavic technical manuals – not on their main website

username: mavic-com
password: dealer

Video on freehub replacement here
Rogue Mechanic

Service them every 3 months to prevent wear. Peasy 10 min job once you’ve done one.