You might need to rebuilt the master cylinder. My son had a fall once, and damaged something in a brake MC, and it felt just like you are describing (like it needed to be bled), but bleeding it didn't help. I bought a rebuild kit, put the bike on it's side (so I wouldn't have to drain the fluid), and had it repaired in about a half hour (no instructions involved). I know that you are talking about a clutch, but the two operate in essentially the same manner.