I've replaced two Airmar P58 "tri-ducers", each after about 400 hours operation, because of the same failure mode. They are designed to auto-level by rocking on a horizontal pivot. The problem is: the continual pitching up and down in ocean swells causes the wire to flex at its entry into the case until it fails, admitting seawater into the case and wiring
and destroying the unit. The manufacturer should have included a stress relief gland to increase the radius of bending at the entry point. I have fabricated one from epoxy
putty on my (third) replacement unit.