If the sleave is tight (often when they are in there for a long time & the piston/sleave is worn out), slide a zip tie through one of the ports while the piston is BDC and poistion the head of the zip tie so that when you rotate the crank the piston pushes the sleave up & out of the case. if that doesn't work you may need to put it in the oven for a bit to warm it up enough to let it slide out.