Your oil pressure is low enough to be in the danger zone, so an oil pan removal and inspection of the bearings is in the near future. It's better to do it now, rather than wait until a bearing fails and the crankshaft gets damaged. Then the fix goes from a few hours' labor and a few hundred dollars' cost to an engine removal and thousands spent on a major overhaul. Your choice, and doing any other sort of diagnosis won't change the cold hard facts. Oil pressure loss can be from worn connecting rod, main, and camshaft bearings. Rods are easy, mains are not terribly difficult, but cam bearings require a major disassembly down to the bare block. That's major rebuild stuff. Oil pump problems? In 60+ years of rebuilding hundreds of engines, I've seen two oil pump failures- - - -both caused by debris that blocked the relief valve open and dropped the pressure to zero.
Remember the old ad that said "Pay me now or pay me later"? That's your situation, and the "now" needs to be "soon"!
Jerry
