im quite ashamed to say but ive tried a number of thing to stop a coolant leak from the thermostat, ive put a new gasket on it, ive tried using instant gasket (rubbish). i havent got a torque wrench but ive tried different levels of tightness. my next step is to get one. other that the torque could i be doing anything else wrong? i grease the gasket. i try to make sure the block is clean. is there a common error people make?