1974 225s, Ford 302: I just got this boat and need to replace the two bottom anode/gimbal housing to transom bolts at the bottom of the assembly because on one of them the bolt for the zinc knob is gone (assumed corroded off). When I tried to remove the nut from inside of the boat, the bolt snappped off after about a 3/4 turn of the nut. I used a drift to drive the bolt out though the transom. My question is what should I use on the new bolt to seal the hole? Does the square part og the bolt need to have direc contact with the gimbal housing?