I have heard that in some boat configurations the motor must be removed to get cable assembly out. Did this just suddenly stop working or has it been sitting for a while. ...Maybe there is a mechanic malfunction (ie something came lose or elsewise binding) rather than the cable being frozen. I'm no expert but guess there is a better lube for the application than WD40. Also, try disconnecting the cable from the motor so you can isolate the cable being the problem rather than the pivot on motor. Mine (Honda) is very tight and the problem is in the motor pivot.
ChuckD
ChuckD