For the Vauxhall pump,   both Offset or Central drive         (not for the aftermarket FAI /   concentric rotor type)  

These piston plungers are well known for clogging up or when worn failing to return to its rest position, giving a loss of Oil pressure. Hence the complete pump is then wrongly  "blamed" for being faulty -  when the actual pump is still fine to continue to be used. 

Keep your old pump working for longer.  

The buy-it-now price is for ONE plunger and ONE spring,    -   three are shown in the photo for illustration purposes only.