no u dont, it does happen, usually with older brakes though, if u could (which u cant) u should pop the pistons out and clean them up to feck, but u cant Ne ways, to get ur piston out of the master cyclinger, undo the 8mm spanner shroud nut and remove the hose and also take out the 3mm bleed nipple u will have 2 tiny acess holes into the master cyclinder from the other end than the lever u need to grab 1 or 2 small allen keys (1.5mm ish) and push them agains the piston through the bleed and hose holes, this will push it al the way out Clean up with Hot Soapy water, *degreser if u have ne* then re-fit with the spring in first and the piston facing so the crator *not pin* is showing outwards. Dont press too hard, it will go to the bottom again and get stuck Mike