Just had it replaced last week, same problem, see here:
viewtopic.php?f=9&t=48980
Went for the single mass fly wheel, beware of the noise it makes bellow 2000rpm, but the zed feels quicker with the single one. If you're doing the whole job, go for the B&M short shifter as well like the one here viewtopic.php?p=642413#p642413 totally changed the feel of the gear changing, very precise and short! Love it!
Good luck!