I think that 25psi at running speed is on the low side. Change the oil & filter if not done recently, so you know it is good quality. Then locate the oil pressure relief valve. Remove and check that it’s not sticking open. If parts are available consider replacing the valve and spring. Finally, slacken the oil pipe union at the gauge with the engine running at idle. Use a large rag to catch the drips of oil, and don’t over-loosen. While you do this the gauge will drop almost to zero, but when you retighten, you’ll have purged any air which may be in the line. If the pressure remains low after that, there may be bearing wear, but it should last a while if you don’t over rev it!
