I had a guy over this week wanting to replace his Milidon single entry cast aluminum oil pump due to it not having any oil pressure after priming it. He had recently bought this 1972 duster with a 440 motor in it that use to be a "drag race car" that had not been started in several years. He was smart enough to prime it before trying to start it but it loss the prime the second time he tried to prime it again the next day and it wouldn't make oil pressure again using his 1/2 inch electric drill motor. I had one used one and one new one on the shelf, he ask me how much I wanted for it and I told him what ever price Summit sells them for or replace it with another new one. He took it home and looked up the Summit price ($339.95)and then decided to look closer at his, I had told him to look at the bypass valve and spring in the pump cover to make sure there was no debris or gunk holding it open.
It had a hunk of silicone holding it opened Once he clean that out his pump work good New motors make metal while breaking in and it is impossible to keep a new motor to clean while assembling them