I'm not sure how the screw got there, but what happened was one of the mounting screws (3 tabs along the top) was too long and punctured the radiator. It was fixed with epoxy and seemed to hold up fine until my tech removed it and the screw pulled the epoxy out. The tech didn't feel comfortable trying to re-epoxy it nor would I feel safe using it on a pressurized system, so a new one went in. Expensive, but peace of mind.
Paragon Products supplied 2 pumps to the <acronym title='previous owner'>PO</acronym> (1 reman, 1 new) and both failed. My tech recommended a Porsche supplied reman unit this time as he said even the new ones are failing these days. Even Porsche supplied products aren't a guarantee as the gasket they supplied with the pump was no good so he had to wait for another. about 200 miles since the "new" pump went in and no more leaks so I'm happy, albeit a little lighter in he pocketbook.