just thinking aloud... the pump that pushes oil around
is driven indirectly by the crank governed by RPM...
so inflight the oil pressure should be extremely stable...
over time it might change +-1 due to oil temp, but
those movements should be tiny as 6qts of oil have
quite abit of thermal mass.

oil pressure for my engine should be between 30 and 60.
but even with a tiny bit of oil, the pump is going
to try to keep the pressure constant... so the
first sign of low oil might be a fluctuation in oil
pressure, likely because of tiny bubbles in the oil
or very short un-porting of the pump draw line..

note to self: the prop requires oil pressure
to work..

another note to self: if the oil preshure is changing,
find the closest airport.