Evan Carew wrote...

Yeah, I've been to those exact pages, & will note for the record that
none of those pages mention an o-ring for sale...

You might note that none of the fittings pictured are
simple 37 deg flare to NPT fittings - there's
a wider bearing surface for the O-ring/NPT end.
The Lycoming standard solution does _not_ appear to
be to stuff an O-ring over an NPT fitting, cut down
or otherwise.

Dave 'field mod' Hyde