Cat 420 E e stick

hi I have a 2003 cat 420 e and the cylinder that makes the extendahoe move out and in is leaking from what looks like a fitting that goes inside it. How do I get to that cylinder? I'm thinking maybe I have to remove the whole back on the boom. Also can I without hurting anything so I can use the machine for now cap off the line that controls the extendahoe until i can repair it? Thanks