Mark Lipton states:

"Teflon is certainly unreactive enough, but it might be too plastic to
keep a tight seal. For instance, the teflon tips to the plungers of
Gastight syringes that we use will deform enough if the plunger is
stored in the barrel to abrograte the seal of the syringe (that seal is
quickly restored by banging the plunger tip on a countertop several
times -- very plastic indeed). That happens over the course of a few
days, so a Teflon-lined cap would surely deform and possibly lose its
seal during the time needed to age wine."

I never used Teflon syringes at work, but I know other types often had
problems with the seal also, perhaps for different reasons than for
Teflon ones. We used pure tin foil in bottle caps, and it seemed to work
very well for many things. However for some very nasty things that will
react with tin, Teflon discs worked very well if you tightened the cap
down well, even for very volatile liquids. In addition, metal pipe
threads sealed with Teflon tape held up well and did not leak, even at
very high pressures. The experimental thermodynamics people did use some
pure gold gaskets in some of their combustion bombs that could produce a
very high internal pressure. If gradual flow did tend to unseal the cap
over a very long time, a metal disc behind the Teflon disc and a small
sprong between the metal disc and inside of the cap would help keep
pressure on the seal if need be. Again, I am talking only about wines
that are to be kept several to many decades. If you are stuck with old
bottles that have very old corks, you can always remove the capsule,
clean the top, and dip it in wax several times. Of course this would not
do for wine that is to be resold. I have a few very old bottles waxed.
If the bottle is to be kept in a cool cellar and not moved, USP beeswax
works well and is easy to apply and remove. Many old vintage Madeiras
solved the cork problem by sealng the top of the bottle with a heavy
coat of sealing wax instead of using a metal capsule. I have a few very
old bottles thus sealed, and the wax likely is the only thing that
prevents the bottles from leaking.

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