Finally, if people would handle cylinders gingerly and not hold them by
their pushrod tubes, the damn things wouldn't leak. Having to use
that beading tool to seal the tubes inside the cylinder head just means
the cylinder was abused by someone.

Amen to that. However, the aluminum head expands at twice the rate of
the steel tubes (the coefficient of linear thermal expansion) and this
tends to leave the tubes a little loose when things are hot. I don't
know if Continental relied on the metal-to-metal seal when they
manufactured them, or if there was some sort of sealant used that
crumbles or disappears with age. That's why I use the Loctite, after
the cylinders are installed so that the tubes won't be moved anymore,
and the Loctite, being plastic and having a much larger expansion rate
than even aluminum, keeps things sealed up all the time. Loctites reach
their maximum strength at around 300 degrees, too.

Dan