Set of 3x Piston Seals for MK4 Hill Pump. The classic symptom of a problem with this seal is resistance on the upstroke and tendency to recoil back downwards. The piston seal is the workhorse of the pump and it's life can be dramatically shortened by overheating and a lack of lubrication. To maximise the life of this seal please follow the advice on pumping and lubrication in our instructions.