I like this idea of sealing valve pouches with PVC-E if it works.
Will PVC-E pass the "time honored" test in the future (stay airtight
and very flexible 15-20 years or several decades)?

I do know it doesn't pass the "historical accuracy test" -- important
to practice as much as reasonable -- but some people go "overboard"
in my view.  It's admirable to do things in a historically accurate
way all the time; I respect that.  Some people just feel they have to
be the "player piano police", condemning anything not originally used.
PVC-E passes the "reversible restoration test" because it doesn't touch
the wood.

I've been drawing the rubber cement into the pouches with the tracker
bar pump or suction box because the solvents (particularly in the
thinner) are very toxic.  The PVC-E is water soluble and one could use
the "suck tube" by mouth method which I think does a better job sealing
the pores in the leather.  The PVC-E doesn't touch the wood so there is
no potential problem for a future restorer removing the stuff.

I've mentioned numerous times here on MMD that "furniture refinisher"
of any brand will take off PVC-E.  Nonetheless, people continue posting
here that PVC-E cannot be removed.  The real problem is, who knows if
anything will be available to remove the stuff in the future.

I like to use PVC-E for the overlap on the hinge end of pneumatics
(air motor, striker and accordion pneumatics) because of its superior
flexibility over hide glue or fish glue.  I gotta say, it's such
a tempting idea to seal pouches with PVC-E.  But, while I believe PVC-E
will remain flexible, I don't know for sure.  I believe it will remain
more flexible than hide glue but maybe not rubber cement.  I'm gonna
"play it safe" and stick with the rubber cement on pouches (pouches
must remain flexible and airtight to work properly).

Does anyone know _for sure_ that pouches sealed with PVC-E remain
flexible and airtight enough for several decades?  I'd love to see the
evidence because I'd rather use PVC-E if it works.

Bill Maguire