If you are getting 15 to 20 pounds of oil pressure on start up you are on the high side. To know that means you do not have the correct gage.
5 pounds of oil pressure is not all that bad for that engine with a lot of time on it. It would be a good time to change the oil and filter to have a base line of knowing what oil and filter you are watching. You most likely would not need a (new) oil pump. It might need the pump cover cleaned up some time in the future.
The cover on the right would bypass oil and not give proper pressure or hold a prime.
The cover on the left is how you want it to look before replacing it.