Sod that just buy another pump all the messing around it may continue to keep playing up if you get it going.
+1
You should always have a spare pump in the van anyway IMO, its one of the few things that can stop you working completely.
+1
always have a spare van too, because that's another one of the few things that can go wrong and stop you working completely

tbh there is very little to go wrong with a quality pump and a shurflo is one of those (many still are using pumps 5+ years old), far more likely to be the pressure switch or a wiring fault.
In a perfect world and enough money we would all have enough spares for every eventuality and most likely never need them

Simon