Kick up stink to your dealer, thats the only way to get them to understand where your coming from. Ok yes you put the bike away for a while and didnt wash it, which is what you need to do with any bike when your putting them away. But for a bike to be corroded as much as yours i would say is not on.
If your dealer doesnt bit, either try another dealer and if worst case, take photos and send them off with a nicely worded letter to yamaha themselves.
Should get them to shift on it.