The viscosity numbers mean that when the oil is cold it will flow as
well as 15 weight and when hot won't be any thinner then 50 weight. I
would doubt that is your problem.

You mention that "the pressure dropped off and the light came on"
which implies that both the gage and warning light circuits are
working correctly.

When you say that the oil cooler tubes are "almost scary clean" what
does that mean? The oil side should be full of nasty old engine oil,
it is, isn't it?

You say that you checked the oil pressure valves - plural? If you can
get at the oil pressure relief valve try sticking a washer behind the
spring and see whether that raises either the idle or full throttle
pressure. If it does then either the pump is worn or the spring in the
pressure relief valve is getting weak.

I am with you on the gauge and warning lights being correct. There is
actually seperate senders for both. I was looking to get a mechanical
gauge sent out here, but I am in no rush to do that right now.

I must admit that I never looked at the oil side of the cooler (stupid
move). I was focused on the water side as a friend had 50% of his
tubes clogged. I guess I hoped my cooler looked like his, so I
blanked out on looking at the oil side when I sas it was so clean.
Now if the oil side was gummed up wouldn't my pressure be higher? Or,
would the cooler just get bypassed and overheat the oil?

There are two pressure relief circuits for this engine according to
the manual, one is for piston cooling oil and the other for engine
cooling oil.

If the washer raises the oil pressure, should I leave it there until I
can get parts? Or, do I need the parts right away if the pressure is
acceptable?

Kurt