I get an oil light exactly at 1800. No high and no lower rpm. Also, the car must be moving (in gear or in neutral, doesn't matter) and the RPM must be at 1800 RPM for 2 seconds or longer. Just being on 1800 shorter then that doesn't turn the light on.

I was suspecting maybe crank case pressure was dropping and thus causing a momentary oil pressure drop. So I changed the crank case PCV, combination valve, and the two check valves on that system and it didn't change anything.

I've had a shop check the oil pressure while the car was in park, all checked out to factory specs, no issues with oil pressure. I'm about to hook up an oil gauge and drive the car until the oil light comes on to see if there is a pressure drop.

Before I do that, did you ever get your oil pressure light issue resolved?