Here is the email I received from him this morning:
Hi Shaz, I worked with live leaches. kept one as a pet Larry the leach. He would have dinner with us . We would feed him raw meat. The Scene was shot on stage in a heated water cave set. The gag was the science character was supposed to shock the leaches off. by using two wires from a battery they had. We had live and fake leaches. Steven Spielberg helped me a bit by handling some. We had trouble making them stay on I seem to recall. It was fun and the actors were great. All the best, [steven kutcher]
You're welcome guys.
Merc, At the end of the oath scene (deleted), Andy screams "leech!" and the goonies discovers that they are covered with leeches. Data removes them by electrifying a puddle with a battery.