fantic240motor

Not particularly a big or difficult job depending on your mechanical ability. 
 
All the parts you'll need are a set of seals and new oil. Only special tools other than a vice with soft jaws or Black and Decker workmate is something to push the new seals down into the legs. If not a purpose made tool then an appropriate sized piece of plastic pipe can work okay. Getting the old seals out can be tricky and there's a sequence for undoing the internals to make life easy.  
 
It's a job most owners of trials bikes will have to do at some time.