This seemed like an overly simplistic diagnosis of what could be many different problems. Be forewarned, if you're not comfortable with tools (and wasted time) taking on a brake problem like this should not be taken lightly. Once you crack off that master cylinder, you're looking at a lot of air in those lines needing to be properly bled out. If you don't know how to do this at home, you're in trouble...

While its deffinitely a good idea to know what you're getting into, bleeding the lines is not that complicated process. Just grab a buddy to pump the brakes while you crack open the bleeder valves a few times. Just remember to bench bleed the new MC or you'll never successfully get the last of that air out