I am not a lawyer, but I believe that there is a legal principle called "agency", whereby an employer can be held responsible for a promise made by an employee, especially if it is a promise that a purchaser would consider to be credible.. I suppose that in law an employee is considered to be an "agent" of the employer, acting in its behalf. I guess this approach would be negated if the warranty expressly excluded water damage. You might want to write to corporate headquarters telling them that you would prefer that this matter be settled amicably, but suggesting that you are considering taking this matter to one of the media consumer complaint services that might make the complaint public. You might also tell corporate hq that there will be very favorable publicity for them on a fishing website if they settle this matter to your satisfaction. However, you might be walking a fine line between legitimate pressure and blackmail if you threaten or imply negative publicity for them if they are not cooperative.

Good luck, and keep us posted.

Bob