A leaking vacuum advance would be a steady leak once throttle is opened enough for it to see vacuum because it is operated with ported vacuum giving a wee bit lower than normal vacuum reading. This would not cause gage needle to quiver. Quivering is caused by unequal intake manifold pressure between valve events due to a stuck, burnt, or maladjusted lash allowing gasses to backtrack into intake.
Check your valve lash first, one valve not fully seating would cause the fluttering readings you are getting, inconsistent lash settings will also change overall vacuum readings, poor idling, and bad performance.
