Hello! My Kunzer WK1010 shunter lifter no longer builds up pressure, what can that be? Error description: – If you close the ventiel (turn it) and pump up without load, the arm goes up very quickly. – If the jack is pushed under the load (vehicle) and you pump up, then the arm goes up to the load and stops, no lifting process! It is as if no pressure is built up. You can hear no noise, even if you pump faster, no movement. It is whether the pump e does not produce any pressure, but without pressure promotes oil (because the arm goes up without load). Does anyone know advice? What seal can this be, does someone have a hydraulic plan of the jack? Thank you!