Not long ago, I bought a 2000 Tracker that has what appears to be a Humminbird Pro Angler 400SX fish finder on the front. The transducer is mounted on the trolling motor, and the unit seems to work OK. When parked in my garage in warm weather, a thin black, tar-like liquid drips out of the transducer through a small round hole at the back of the transducer and forms a small puddle on the garage floor. What is this liquid? Does it need to be replaced, and, if so, with what? I know I should just buy a newer, more modern unit, but for now, I'm trying to keep expenses down.