Agree with dhein. Grab the sensor at its base by its wires (carefully) and rotate the sensor right/left or clockwise/counterclockwise several times until the glue is loosened and the sensor lifts off the hard drive. Works like a charm.
When it's time to attach the sensor to the new HD, press it in place fairly firmly and hold it there for 20 seconds or so. Then reapply the tape.
