I have had similar problem, very irritating - pump replaced (ESR3926) but still does not always run. Main dealer says plug is not spare part - it only comes with the pump.
Replacing both the fuel pump relay and the fuel injection system relay (both AFU2913L on my vehicle) seems to have improved the situation considerably, so might be worth a try (about £15 each).
If you identify a source for the plug please post - I would still like to replace the plug which dealer filled with waterproofing grease, and could be resulting in a poor connection.
Strangely, releasing the fuel cap sometimes gets pump going!
Angus