I am afraid I don't know other than it wouldn't pressurise. Dave Robinson said that he trie everything he knew and still nothing.

I was experiencing similar symptoms after the bike was sitting for a month, a bit of advice from Nelly, and I bled the slave cylinder, then the master cylinder, and all is well again! :D

I've just sold my '04 RSVR for this reason. Got fed up bleeding the clutch every 500 miles or so. A combo of air and water in the system. Lever gets stiff causing arm pump. The gear change gets so notchy your foot aches and eventually you can't change gear.

My 999 is like a knife thru' butter by comparison.