You should be able to buy that part and the rod (?) from Mojo on their own. Then just fit them. They'll be an exploded parts diagram somewhere that may help, or just give Mojo a call and explain.
Thanks, been in touch and apparently its an old part they don't stock so would need an entirely new cartridge which is over £200 alone plus fitting/service over £300.
Probably not with it, the forks work ok anyway so maybe I will get by without this adjustment.
I guess if anyone has an old/broken f80x they want to part with so I can try swapping the part over, I'd be interested.