They all do it mate . The pads rust onto the disc . New calipers are very expensive , about £120 on and exhange basis , sorry thats for a refurbed one. If it really is sticking it will ne the handbrake mechanism , the adjuster screw can rust inside . Its a bit of a ballache to sort to be honest , when you pull it apart there are 5 sprung washers inside that are a right b*tch to get back in , you can alway leave one out though . Take out the adjuster screw , clean it up with some emery cloth , grease it and put it back together then it should be ok .