Does oil come out the tailpipe?
If it does:
PCV Valve
Valve Stem Seals
Bad Oil control rings on the pistons
One thing which could set it off and make the problem repeat itself is vehicle position, if its parked up on a hill does it make it ink? If so then its either
PCV valve thats located at the back of the engine that has a faulty spring and is stuck open or Bad Oil control rings or a bad valve stem seal.
A bad valve stem seal is usually a temporary problem though upon startup, bad oil control rings will cause the problem to be random when driving.
A bad stuck open
PCV valve will show a sign of oil and dirt stuck all the way through the intake manifold, a visual inspection of that will tell you, clean the intake manifold out and see if the oil comes back. If it does, use either an oil catch can or replace the
PCV valve and see if that fixes it.
Bad oil control ring,
pcv valve or valve stem will show signs on the affected piston by fouling the spark plug of that cylinder.
I would start by pulling the spark plugs and see if they're fouled by oil.
If position doesn't make it worse:
You'll need a hoist and a really bright flashlight for this.
Hoist the car up and check the entire engine bay of the car for any oil seeping around somewhere. After all of this time it will show up as dirt sticking to the engine. I would be checking front and back main bearing seals and the engine sump seal. If theres oil pouring down the side of the engine then it could be either a valve cover seal gone or a head gasket gone.
My mums V6 1MZ-FE camry has the same problem. We just live with it.
If you depend on this car you could conceivably install a buzzer for the low oil pressure light in the dash so at least you get a visual and audible warning of low oil pressure.