1990 WWestfalia brake failure troubleshooting - suspected master cylnder failure

What is your question?

Vehicle had been sitting for a few weeks. Started it up, put it in reverse, gave it some gas - felt like something was bound up - vehicle not moving??? check e-brake - off. Gradually/slowly gave it more gas - BOOM! It broke loose and now no brakes! Checked under the vehicle - no fluid on the driveway. Suspect master cylnder failed but would like some feedback from someone with more experience.