D17 Oil Pressure

I have a 1958 first series D17 that starts and runs like a champ. After about 20 minutes, though, the oil pressure drops. I changed the oil and made sure all the seals/gaskets were right, had the right filter, had the 'stem' inside the filter, etc. (per some earlier posting recommendations on the subject). That helped a bunch - oil pressure shot right up. Still, 20 minutes later it dropped to almost nothing. Bad gauge? Any other thoughts or suggestions? I've got a couple general oil leaks and drips, but nothing dramatic.

Thanks!

I once had a car that had zero oil pressure after warming up. I added one can of STP to the oil and the pressure would only drop to 20 when warm. At low RPM, it was still pretty low. STP today is not as viscous or sticky as it was when I did that so it doesn't work as well. Back then, the engine had to be at operating temperature to add it. It is still worth a try.

Beyond that, you'll need to replace cam bearing and all crank bearings. Usually the crank can be reground and under size bearings can be purchased.

I'm not a proponent of most of these oil additives and believe some do more harm than good. But STP has always served me well.