Re: In this case, it's not the technology.
You missed one more. Pulling the dusty files out of the dark corner of the brain where they were confined after I got my Chemistry MSc and went to the dark side of IT: Many light metal alloys are not steel, they change with time and some of them quite a lot. Some of it is change in crystalline structure, some of it is oxidation, some of it is dark magic which noone understands :)
Most Al, Ti, Mg, etc alloys (as used in space tech from half a century ago) would have undergone a considerable change of mechanical properties over 50 years (not necessarily bad by the way, Al alloys generally become less fragile and more plastic with age). What would have been well within the tolerances 60 years ago, may not necessarily be usable today. If the pump has any elements made out of Titanium or Al alloys that would have been the prime suspect in my book.
IMHO - this is the biggest FAIL in the Orbital idea. It is not a rocket technology fail, not a control tech fail, not a refurb fail. It is a material sciences fail.