I'm sure someone in the automotive service, repair or parts business will correct me if I am wrong, but years ago when I was into restoring fuel injected Type 3 air cooled VW's, I experienced successive failures of several "used but not abused" fuel pumps. I distinctly recall conversations with the guys at Bill & Steve's in Downey CA, considered a mecca by VW gearheads, that the seals in fuel pumps submerged in gasoline during years of use and then allowed to sit out on the shelf would dry out resulting in failure of what appears to be a perfectly good part when the pump was put back in use. I was cautioned to install new fuel pumps rather than used. I followed that advice and never had another VW fuel pump failure.
I had essentially the same conversation several years later with a fellow named Jerry Piper, the owner of the parts house that supplied my local jeep shop and the other repair shops in the area. His take was slightly different. He had no problem with installing a used fuel pump if you had one but no money for new parts, as long as you realized that the odds were only 50/50 that it would last and at least 50/50 that it would fail at the worst possible moment.
Those conversations were in the back of my mind when I commented that if OP's fuel pump is working he should leave it where it is.