There was a thread on fuel pumps a while back that included the opinion
that you shouldn't buy and store an SU pump 'cos the contacts would
foul up. I didn't comment but did wonder what happened after purchase
by the end user that was so different to what happened between
manufacture and said purchase.
I bought a new SU pump last week as a spare for a forthcoming trip to
France, and there in the manufacturers blurb it says "check the pump
before fitting and if it fails to operate clean the contacts, this will
not invalidate the warranty. Pumps should not be returned as faulty
until this has been done" or words to that effect.
You live and learn.