sorry to piss in your fire, but standard or new internals arn't avalible for the mantiou carbon x verts, it took me 4 weeks to get hold of a top cap for my old set (and this is about 2-3 years ago) i really doubt you can get parts now.
because of the poor materials they use for the internals, ie, a lot of plastic, and piss thin alloy, and the fact they are closed oil bath (piston) it would be difficult to service anyways or make improvements, the piston itself is not even an inch thick and the whole thing holdes practcaly no oil.
the best you can do is, take the lowers off, clean the inside of them and the stantions. put some mantiou fork grease round the seals, put back together and put a few pumps of grease in the grease ports.
there an old classic, they needed a lot of tlc then, and even more so now. probaly the highest maintanence fork there was.
if your not to sure what your doing ring good ol tim and see if there is anything he can do,,, there are no upgrades avalible for this fork, the best you can hope for is a slight improvment inn the perfomance.
(is it obvious i owned a pair? and taken apart many times

)
gonch