Use a multi-tool or circular saw to cut away the outer fiberglass skin . Carefully pry it off to reuse later if possible.
Coosa Bluewater is a fiberglass-reinforced foam that is 100% rot-proof. Cons: Significantly more expensive than wood. grady-white-transom-repair
Tilt your outboard up and apply downward pressure to the lower unit. Any visible movement or "smiling" (the gap opening between the motor and the transom) is a red flag. Use a multi-tool or circular saw to cut