Oil pressure issue.

[Waterloo]

Like Signature stated, oil filter first, rule that out. I would also change the oil pressure sensor out too, they do not last forever... I would also pop the valve cover while doing the filter and sensor. If those items check out and there is still an issue...

It sounds like something spun... Or the lower end is wore out. If it is the lower end, you could do that and see if you can squeeze some more life out of her, that is if the cams check out up top and the liners are still intact. I only say that not knowing your financial situation.

If the top looks good, no chewed up cam lobes/rollers, you could roll in new bearings on the lower end, but your real issue will be the wrist pins in the rods, one of those fails, you could/will ventilate the block. If you have to remove the head, you should in frame with that mileage. That is a one time use head, once off, it is scrap, especially with that mileage.

At what mileage was the M and M installed? If several years and hundreds of thousands of miles ago, you could attempt the above and hope everything holds together. If not long ago, I would be hesitant, and go the in frame route.

If you can afford an in frame, I would make an appointment with Mr Hag.

Me, if the cam(s) are chewed up, or it needs new bearings in the lower end, I would in frame, because there is no such thing as a million mile + EPA motor out there in the Cummins family.