Vacuum gauge is your friend, - vacuum leak is constant, fluttering guage indicates fluctuating vacuum, a single, or many out of adjustment valves will cause that, as opposed to a constant leak, like a pcv = steady guage .
jmo
This site had vids of various guage symptoms, they don't load on this pad, hope it does on yours.
http://www.secondchancegarage.com/public/186.cfm