So I ordered the Pierburg pump and while waiting did a pressure test on the Delphi and sure enough only about 60 PSI head pressure and pump makes an awful sound at that point so looks like the pumping elements are worn out and I was fooled a bit by the burnt connector. Delphi bragged about having made the motor better, and the check valve seemed to hold nicely too but I guess that doesn't matter much if the pumping elements are still a weak link.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)