A good strip and clean every year works wonders. If your not proficient in the mechanical dept yourself, a decent independent will do it for £20 (takes them minutes), and youll notice the world of difference.
You may have done this, but put some spacers between the clutch cover and casing as this helps expel dust etc..thus getting rid of mr screechy !!!!
Hope that helps.....incidentally my 888 has just come back from service and the clutch is on its last legs. I am told a genuine duacti one fitted is around £300(or £700 for a bucci slipper clutch..yum yum !!)