My parents' [then] new ensuite plumbing started leaking ~6 months
after installation. All I had to do was take apart and remove the
PTFE from the sealing faces of the compression fittings (I was
lucky - once used, it will often deform the sealing faces so they
won't seal again, without bodging it with more PTFE).


That can only happen with a very extreme bodge, though. PTFE is *very
much* weaker than metal, and one or two turns over an olive will just
extrude into the space alongside the "line contact". There has to be
enough PTFE to completely fill all the available space, so that you
are generating hydrostatic conditions within the joint.


Why get it anywhere near an olive?