Oil pump questions

I know that the topic has been covered before and I apologize for plowing the same old ground but here I go. The oil pump on my '23 Hudson looses prime between start ups. If I prime it through the pipe plug at the front of the pump, the gauge registers immediately upon starting. If I don't prime first it takes a minute or even more to register. After I shut the engine down it can take two hours or more for the gauge to fall to zero. What is going on with my pump and gauge? My guess is that the issue is with the pump rather than the oil pan troughs but I have been known to be wrong before. In fact I am somewhat famous for being wrong. Any illumination is appreciated. Zeke