As an automotive engine rebuilder. I would suggest if you have a higher time engine, not to overlook the possibility of excessive wear of the connecting rod bearings. They take a beating on every power stroke. A few extra thousands of an inch let’s a lot oil squeeze out. The oil pump cannot overcome the extra flow and therefore will not develop the pressure. I own a M20E with a 360A1A. It has 1900 hours and my oil pressure is 50psi at hot idle and low 60s at 2600rpm. We installed an ESI MVP50. When the pressure is under 60psi the yellow warning light flashes. Annoying! I added washers to the pressure relief valve. It didn’t make any difference.