99 nomad 1500 clutch problems

[Vulcan-al]

Ok so twice now I have lost my clutch. the first time I was on a road trip and went to leave a town that I was in and I had no clutch. I found that once I took off the cover for the resouvour and pumped the lever 3-4 times I got resistance back in the lever. the second time I was on the hi way heading home and I went to shift down and realized that again I had no clutch resistance and was stuck in fifth gear. once I could get stoped and the bike off I removed the cap and compressed the lever a few times and I had gotten back resistance again and it worked all the way home. any ideas on what this might be