Actually the pump was OK, but it was the pickup that was smashed. I didn't realize this until the used oil pump arrived & I could see what it was supposed to look like (intact). Now the pressure pegs on startup, and levels off. Unfortunately, after ~ 10 minutes or more, the pressure goes to zero. This has me baffled. The pressure goes back up if I restart, but doesn't sound too good.any ideas on this?

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1985 300CD 279k
2000 F250 powerstroke