Hello,  So we are still unsure of what the correct answer is...  Please
keep 'em coming! :-) More test results would also be quite interesting.

On a separate note, I would like to add here that it is a complete
myth and a bad idea to make a stack completely airtight.  In fact, it
needs to be somewhat leaky in order for the regulators to work.  They
need a load (airflow) to allow the vacuum to drop if the expression
system suddenly changes from high to lower settings, and also to keep
regulating a constant vacuum without creeping up.

Kind regards
Bernt Damm
Sydney

 [ West Coast player tech Clare Spencer would drill a small hole into
 [ the treble and bass windways of the newly rebuilt action stack.
 [ He said when enough leakage developed then he would cover the extra
 [ holes with pneumatic cloth.  -- Editor (Robbie)