Why is there gas in my crankcase and why is it leaking?

I just bought a 1996 kawasaki vulcan clic 800 and it appeared to be leaking out of the crankcase from the two bottom bolts. I tightened the bolts and it stopped leaking from all but one. (may need replaced) The other problem is that there seems to be gas in the crankcase too!! Why would this be happening and what should I do? I am dying to ride the bike but have to repair this first, please help me!