It takes only 9 lbs of oil pressure to turn that warning lamp off.
Once the engine gets hot much of the oil pressure is lost through the main and cam bearings so the top end where the sender is isn't getting more than 9 lbs. at idle rpm. To drop the pan and replace the oil pump and screen might cure it for a long time.
I guess the first thing to do is install a true oil gauge and see the actual pressure variance from cold to hot.