BTW -

How often do you change oil? Confirm you have a full flow filter (it
reads like you do). Does your oil filter have gray (lead) sludge in
it?

What fraction of the time since you got the engine has been 100LL vs
autofuel? I assume the autofuel has to be 91 octane autofuel to handle
your compression?

Have you ever tried to do a mag check at cruise? (i. e. could one mag
be somehow intermittent at temperature?).

Be sure to check inside the rocker covers to see if the rocker shafts
are wearing on the cover sides. I found one (but only one) in my 172M
(1700 TT over 31 years) that was worn substantially. Later shafts have
a nylon thrust boss.

You gotta post what you find. THX