Tony,

I had the same problem last spring. Luckily I had an extra vacuum advance mechanism - my old one barely moved the distributor. The good one greatly improved performance.

I might be misunderstanding your question because you also mention springs (for centrifugal advance?).

There is a diaphragm inside the vacuum advance (this might be bad).

http://www.tpub.com/basae/46.htm

Tim