I had problems with syringes for a while. The thin shiny film which covers the rubber plunger comes off when it comes into contact with water (when washed). When that happens the plunger will no longer slide and the rubber bit keeps getting pulled off. Also the measurement markings come off when washed too. My solution was to cover the outside in clear sticky tape and never wash the syringe in water. I just slide the plunger rapidly in and out a few times just to remove any residual liquid left behind. After that i just put it back in the little plastic baggy i keep it in.