If he didn't have oil pressure as much as he has started the engine it would be a basket case by now
No need to scare the guy.
He said his dash gauge is reading normal as it always has. More than likely, that means that he has not lost oil pressure.
Yes, he replace the mechanical gauge in the engine compartment. But it still sounds like a sensor in the safety shutdown system is causing the problem. I'd start with the temp sensors. They're easy to get to.
is it common for the shutdown valve itself to go bad? is there a way of checking it, because maybe the valve itself is bad. just a thought.