Recently my Four Uncles hand pump has been acting up. When I go to pump up the PCP, air is going into the gun's air cylinder, but my pumps outer tube ; the one with the attached handle rises up the shaft when I stop pumping in order to check the gauge pressure. It rises about a foot or so above the base by itself. It's like the pressure from the hose is seeping into the pump to cause it to rise. I took off the main tube and cleaned and lubed the o-ring on the check valve to no avail. The pump doesn't leak air and it's able to fill up the PCP. I'm thinking it might be an o-ring issue in the third stage piston rod. Has any member on this forum encountered this phenomena?