You should be able to find a submersible splice kit at Roden or Shields Electronics or one of the electrical supply houses. I wouldn't depend on water-repellant electrical tape in a coral setting. But since this introduces a possible failure point, be sure you have a GFCI receptacle or breaker as the power source for this pump (should be what all of us have, anyway).
If you are looking for a pump, though, I still have an old Mag 12 pump I don't need that I could let go cheap, but you'd need to buy a new impeller and live with a slight leak because of a couple of stripped screws on the housing (not a problem in submersible setting).