The kink in this mystery lies in the fact(s) that you're running an eighth mile and dropping pressure like you were running out of oil, but . . You still have oil pressure. Not a lot, but . . some.
Generally, when you run out of oil, the pressure goes completely away or the needle dances. Your pressure doesn't just taper off or drop to a new level.
So, it could be the guage, or it could be the pressure relief spring in the pump. It could also be where the oil pressure line is tapped off of . .
Of course these, again, are just SWAGs because we don't really have enough information. Nor do you, apparently, although it's better to ask now than when the rods make new windows and you end up with a puzzle . .
Pull the pan and look there first. Generally, it should be pretty simple, because short of the Ford Cleveland (Milwaukee), oil systems on internal combustion engines are generally pretty simple . .