I have a 1975 172M now at 1700 hrs TTSN that has never been open except
for the oil pump AD. Oil stays clean using mostly autofuel, with
steady consumption of 35 hrs/qt, compression is good (never has been
great), and past oil analyses have always been excellent. The engine
is smooth, and I don't plan to overhaul it until there is some sign of
degradation. The hours went on somewhat faster when new than now, and
the oil only gets changed annually now.

I bought it new, know its exact history, cruised it at ~55% power, kept
in a low corrosion environment (MN and WI), and preheated always and
only before cold-starting it. Not for sale though.