I had a larger slave cylinder fitted just after I got the bike because the effort needed to operate the standard clutch played havoc with my arthiritic hand!!
It was bought from & fitted by Casoli Moto in East Barnet & has made a big difference (officially 20% reduction in effort) in operating the lever. It was about £110 plus fitting & comes with a 10 year warranty against seal leakage.
Here's the link -
www.casoli.co.uk